For the good part, most areas that arnt green yet lack arguably just one or 2 animals that are popular on their own and so are highly likly to get to green "by accident" with for example arabia going to green with the hamadryas baboon, which coincidentally among the most popular picks left
For my 3 highest priority regions i wanna start top to bottom with argentina/southern south america as theirs only one animal from the other sides of the andes id consider important.
This is the last red region in the game and imo no region should have nothing with only the cougar currently contributing to the wild life together with the 2 domestic camelids and if you wanna stretch a little the african penguin and californian sealion as stand ins for the humbolt penguin and south american sealion.
Thankfully this region doesnt need much with only 2 very important animals and 5 more that would be neat to have:
Essential Tier (Animals that are needed to get past yellow):
1. Arguably the most important addition when looking from a regional perspective not just for southern south america but in general is the patagonian Mara. Its a unique rodent that fills the role of an ungulate, is omnipresent in zoos and is arguably the most iconic animal from the region. It also fills south americas biggest hole structure wise, as our current selection lacks any real filler animals to dedicate a large space to that isnt a camel. It also would work well as a habitat mate to the other herbivores of the region like the tapir, camelids and capybara so its just all around an amazing addition that aces every category.
2. Less exciting but still important, the rhea compliments the mara greatly aswell as finally bringing a non camelid filler animal for south american areas. It would sadly be the americas first bird, but still bird is a bird and even if it looks mostly like a female ostrich it still deserves to be in the game for the value of filling actual space in south america and being just like the mara able to be mixed with more or less everything that wouldnt try to snack on it.
Great Tier (Animals from this region that add something new and desireable for the entire game):
3. As the outlier from the otherside of the andes, the Southern Pudu would be the games only representation of the temperate rainforest of south western south america and add a small deer, being something new for the whole roster. The Pudu has more or less all the same qualitys of the mara but just less good. Its a small filler animal, the most iconic from its region and a great habitat mate, but it does all the jobs less good then the mara, is less iconic, from a region many people most likly wont care if it isnt represented at all and is an ungulate instead of a rodent. Still this is a solid A Tier animal that would greatly enritch any pack its featured in.
4. An animal that people often forget as a possible habitat animal is the black and white tegu and while its actual range into the southern pampa of south america isnt that large if we look at a map its still part of the animals listed for that category so it felt wrong to not include it. Theyd fill the important niche of finally another habitat reptile that isnt apar of any of the 3 groups we allready have and would be the first lizard for the americas. As the largest tegu with a lenght of 70 cm to 140 cm, making them on the smaller side of animals in general but still completly in the range of potential habitat animal, which would be very usefull for indoor terrariums that arnt exhibits, while also being reasonable outdoor creatures.
Good Tier (Animals that are very neat for the region to get it from green to blue but not much more):
5. A duck. Yeah we gotta have those and like any other region on the planet there are a few common in zoos, most notably the white faced whistling duck, white cheeked pintail, rosy billed pochard, red shoveler and cinnamon teal but this list could easily be continued for atleast 5 more ducks. A duck wouldnt make or break this region but it certanly would be a nice addition. The reason they arnt higher on the tiers is that a duck would improve any region in the game but only some ducks would qualify to be sensible "first ducks". Sure the rosy billed pochard is extremly common in captivity and a beautiful bird and any duck would still be a massive improvement but there are quite a few ducks id choose over them if i had to choose just one. The only one here qualifying for a first duck would be the white faced whistling but its also the one that is the least based in southern south america so id felt wrong to put them as important to the region when there are defenetly better ducks to represent this region in particular.
6. We might allready have its domestic version, but the guanaco still got some things to offer to us. Besides it being neat to have both wild and domestic for specific or even interconnected displays as a demonstration of domestication it also would neatly tie up most of the southern tip of south america, but as it would be our 3. camelid i cant say its that exciting or even important for the region as substituting with a lama is just that easy of a solution.
7. While i mentioed before that the californian Sealion is a decent stand in for the south american its also not a unreasonable addition. Unlike the humbold and the african penguin the south american and californian sealion are instantly able to be differentiated by the glance due to different size, color and the males quite prominent mane. They are also the third most commonly held piniped in captivity so thats also something neat. Overall i wouldnt call it needed but if we get an animal pack id rather get them as a clone as most other non birds or monkeys. Still as they are able to be substituted reasonably they are stuck down here as the "least important" addition in my eyes. Still neat though.
If wed get all 6 it would be hard to argue that southern south america is anything but blue but even just the two essentials would bring it up to a reasonable good ranking, which is why im still optimistic about reaching it. Overall a southern south america animal pack would work out surprisingly well, add in the ornated horned frog (pacman frog) and we got a full and not to unreasonable pack to represent the non tropical parts of south america, which currently got essentially the cougar and the two domestics as their only representation. Ofcourse that pack wont and propaply shouldnt happen as it completly ignores south americas biggest sore spot known as monkeys but its still fun to think about how much this area still has to offer.
On the other end of the spectrum is tropical south and central america.
To keep it short whatever animals they add, if there arnt 3 more monkeys this area will never be green. This might sound harsh but with monkeys and parrots being the most important zoo animals from this area by far and often appearing in zoos high both in number and species and parrots being pretty much of the table monkeys need to carry their weight. The area needs atleast one monkey larger and one smaller then the capuchin aswell as a 4. extra to even scratch at the diversity of south american primates. A set up of capuchin, howler, spider and tamarin would most likly be the best, but especally the white faced saki and a titi would also be great candidates, not to mention the fact that theres not one but 3 fan favorite tamarins that all 3 deserve to be in the game. Besides monkeys this area needs some birds with the holy trinity of scarlet ibis, roseate spoonbill and white faced whistling duck being a good start to represent south americas tropical wetlands with birds that fit the way habitat animals currently work, the coati is a must as another omnipresent animal and our first not cat or capuchin south american climber and there are also good arguments for the agouti and ocelot as nice filler fluff, but the general reality is that its to late for this region. This region simply will not be green because the lack of monkeys is that crucial so it also doesnt make sense to lay all the animals out imo as 3 monkeys on their own will make this area green and while atleast the coati is nessecary for blue you could reasonably argue that wed reach blue handily once we got another 3 monkeys. Monkeys are just that important to the zoo identity of this region and im just not seeing it happening, especally as frontier will most likly waste slots on animals like the bush dog where its like neat, another dog, hurray, but what about the animals i actually build a south america area for?
No matter how you slice it, every other animal is just extra fluff compared to the monkey issue and while some are better then others with the coati and the holy trinity being all S tier additions, they wont be what this region is fundamentally missing, just very amazing extras.
Lastly and least i wanna touch up on india.
Of all the regions besides the 2 mentioned before its the only one that isnt incredibly niche, but it still got its issues called "filler animals". Since the base game india allready had most of its biggest hitters but was lacking in small animals, monkeys and filler ungulates and as everywhere birds, but with greater flamingos and peafowl living here its not that bad. Its issues where gently and indirectly adressed over time with the dhole, small clawed otter, striped hyena, caracal, sloth bear, water buffalo, wild boar and takin, but as you can see the animals where all either small to mid size carnivorans or bulkier ungulates.
If you ask me (which i assume you do since your still reading this long post) all of indias issue get solved if we get 1 or 2 of each category, with 2 in total being enough for green and 4-5 for blue so lets look at our candidates:
For Ungulates the represetation of actual grassland ungulates is quite lacking and not because of a lack of choices. Between all the different deers like axis, samba and hog deer to the different indian antelopes there is enough to choose from but imo 2 stick out like a sore thumb. Those 2 are the blackbuck and nilgai. This might be a take as cold as the antarctic winter, but these two in combination would be completly sufficent to fix indias and to a larger extend asias ungulate issues. Two very different looking ungulates, one slim and agile, one large and bulky, both iconic and recogniseable in their own ways, both looking incredibly different from the other antelopes in game, both being commonly held in zoos and both looking great next to another make them a no brainer choice for the indian ungulates. If wed choose just one the blackbuck wins out, cause while the nilgai is more unique looking in general next to the other bulkier ungulates we currently have for india the contrast of the slim and agile black buck just wins out in regional diversity, which afterall is our goal here.
Talking monkeys, there are 3 that immediatly come to mind, the lion tailed macaque, the gray hulman and the rhesus macaque, with the last one directly getting the boot again. The rhesus macaque might be the most iconic and historically important of the 3, they are the most similar to the allready in game japanese macaque and while directly differtiateable from them due to the lighter skin tone, shorter less fuzzy and darker fur, they still are clearly the least "cool" choice here, even if they tend to get more hate then they deserve. They would be a fine addition but with us being so short of monkeys we arnt shooting for fine, we are shooting for atleast good.
Lion tailed macaque and gray hulman meanwhile are completly up to personal preference. Both look unique and would greatly work together to expand the asian monkey diversity but as we know that frontier most likly will just choose one the question is the macaque with a beard, conservation story and a tail with a very limited range or the gray langurs larger range, being a langur that isnt the nose monkey and larger range of biomes.
Lastly birds the choices are easy, to get the most out of two we need a waterfowl and a pheasent. What a good thing that the grey white pelican lives in india. It and the greater flamingo might be far more associated with africa but with both also occuring in southern europe and asia they make for quite the power couple. For a more india specific animal we got the barheaded goose, the most commonly kept exotic goose in captivity and known for migrating over the himalaya between india and the plains of central asia, making them a great rep for all 3 regions. Also as a more "aesthetic" waterfowl then the pelican they fit much better in the classic temple vibe most themed india areas lean in to. For pheasent make your choice and mine is the satyr tragopan. This pheasent is the complete opposite of the blue peafowl in its much smaller size and red orange black color explosion coverd in white spots and iridescent blue around the eyes. This walking rainbow looks not just fantastic but also as different from the peafowl as you can get without loosing any of the flashyness, making for a great addition next to it.