Let's see, to make every area blue... I'll start with the area I'm most familiar with.
Scandinavia
The moose, reindeer, timber wolf, and arctic fox make for a good selection for Scandinavia. I suppose there is only one truly missing species that stands in the way of Scandinavia becoming blue:
1. Eurasian brown bear: Historically the brown bear was everywhere in Europe, but now the only place you can still reliably find them is Scandinavia.
Another additional species is the Wolverine. But if the wolverine was added and not the brown bear, Scandinavia would still not be blue for me.
Western/Central/Eastern Europe
I do not consider this area yellow, as there are simply too many species missing for me.
1. Red deer: This one hardly needs any explanation, as it is the icon of European nature and of course embedded in European culture. The fallow deer is not a replacement.
2. Wisent: The European forest-dwelling bison, brought back from the brink of extinction.
3. Red fox: Another iconic species, and a common figure in folklore.
4. Wild boar: A staple of European forests, but found all over Eurasia.
5. Alpine marmot: A small rodent from the Alps, an area that is currently only represented by the Alpine goat (ibex).
6. Chamois: Helps fill out the Alps some more.
7. Brown hare: The game's first lagomorph, and a common figure in folklore.
8. Mouflon: A European wild sheep species.
9. Mute swan: The greater flamingo is not an iconic European waterfowl species. The mute swan, common in folklore and the bird of love, is.
As you can see, I think the majority of Europe isn't even close to well-represented right now.

Part of this is because I live here of course. If all the above were added, the area would be an excellent blue for me.
Southern Europe
Southern Europe is currently hardly represented at all. The chamois, red fox, red deer, mouflon, brown hare, wild boar will help make it green. But to make this area blue:
1. Iberian lynx: a beautiful species that was brought back from the brink of extinction and is a wonderful example of a successful zoo breeding program.
2. Iberian wolf: a beautiful wolf subspecies that is very distinct from the in-game timber wolf. This would also give us an actual European wolf that looks like the wolves we find here. The in-game timber wolf looks like a North American wolf.
Japan
1. Tanuki: The raccoon dog, while it has a wider range, is very much associated with Japan.
Together with the Japanese macaque and the red-crowned crane, and the wild boar and red fox, Japan has become blue.
Northern Asia
This area is well represented with the already in-game Amur leopard and tiger, wolf, moose, lynx, arctic fox, and polar bear. With the added red deer, red fox, wild boar, and Eurasian brown bear, this area would be very close to blue already.
1. Wolverine: The iconic wolverine is the last missing species from this area, and its largest range is in northern Asia.
East Asia
1. Asian golden cat: a small Asian cat that comes in many color varieties.
2. Tufted deer: The area doesn't have any ungulates yet. This one is small, cute, and has fangs.
3. Pére David's deer: And now there's also a large ungulate. This one is extinct in the wild and is a swamp deer.
Along with both pandas, the pangolin, and the Formosan black bear, this area would now be perfect.
Central Asia
This area is only represented by four animals so far: the snow leopard, Przewalski horse, Himalaya brown bear, and Bactrian camel. There are plenty of animals to fill out this area to make it blue.
1. Saiga antelope: The game's first Asian antelope for the central Asian plains.
2. Kiang: Tibetan high-altitude wild donkey.
3. Yak: Giant bovine from Tibet, that comes in lots of colors.
4. Takin: A big animal from the Himalayas, which sort of looks like a bovine but is actually a giant goat.
5. Markhor: A medium-sized Himalayan goat with large spiral horns.
6. Himalayan monal: I'm not big on birds, but this one is beautiful and I feel like this area needs more small animals.
7. Pallas cat: Speaking of small animals, here is a small cat found in the Himalayas.
India
This area has quite a few animals already, but this colorful and diverse subcontinent still lacks some key species and additional animals to flesh it out.
1. Blackbuck: India lacks its iconic antelope. The first one that comes to mind is the beautiful blackbuck.
2. Nilgai: The second Indian antelope is the giant Nilgai. We lack giant antelope in-game, so this one is very welcome.
3. Chital: India also lacks its deer, so I'm adding two. First is the very recognizable spotted chital. It has a deep rich color and very different horns from the fallow deer. India has lots and lots of deer species, but I wanted one that looked very visually distinct from the fallow, red deer, and pére David's.
4. Muntjac: The second deer is the small muntjac, or 'barking deer'.
5. Lion-tailed macaque: India also lacks its iconic monkeys, such as this one.
6. Grey langur: And another completely different type of monkey, the game's first langur species, and this one is culturally important.
7. Malabar giant squirrel: The game's first squirrel and this one is super colorful.
These animals, along with the elephant, rhino, dhole, tiger, and peacock, will truly elevate India into blue territory.
Middle east
And now we get to the Middle East, which we have nothing for yet. Let's go. In addition to the animals below, there are also the striped hyena and caracal. With these animals, the Middle East goes out of the red into bright blue!
1. Dromedary: The first animal I think of, and the in-game props are already there.
2. Indian porcupine: A very recognizable rodent. Will also help India's representation, but it's mostly found in the Middle East.
3. Sand cat: A small super cute desert cat that is mostly found in this area.
4. Honeybadger: A smaller fierce predator that has a large range in Africa, Middle East, and India.
5. Arabian sand gazelle: A pale gazelle species found exclusively in the Middle East.
6. Arabian oryx: Another oryx, yes, but this one is found exclusively in the Arabian peninsula, with a great conservation effort behind them.
7. Arabian leopard: Yes, another leopard, but this one is the antithesis of the Amur leopard. It is the smallest leopard, desert-dwelling, and pale in color.
8. Hamadryas baboon: A desert-dwelling baboon found in the Middle East and the horn of Africa.
Africa
North Africa
Only two animals for North Africa are in the game right now: the scimitar-horned oryx, and the fennec fox. We already have the dromedary, sand cat, and honeybadger that were added for the Middle East. To complete North Africa, here are a couple more following animals.
1. Caracal: The quintessential desert cat. It also helps with Middle East representation, but its largest range is throughout Africa.
2. Striped hyena: A large predator from North Africa and also the Middle East.
3. Addax: A beautiful desert-dwelling and critically endangered Saharan antelope.
4. Barbary macaque: The only non-Asian macaque species, found in the north of Marocco and wondrously also on one tiny location in the south of Spain.
5. Somali wild donkey: A very pretty desert-dwelling wild donkey species.
6. African golden jackal: The game's first jackal, representing a medium-sized canine predator.
Tropical Africa
Tropical Africa is well represented in my opinion. The only thing that would make it even better and therefore a complete area, are a few monkeys and the red river hog.
1. Red river hog: The widely kept colorful tropical pig.
2. Mantled guereza: A black and white colobus monkey.
3. Preuss' guenon: A terrestrial endangered guenon monkey.
Madagascar
1. Fossa: Madagascar's lemur-hunting predator.
Madagascar really only lacks its predator. More lemurs are welcome, but with the arrival of the Fossa Madascar is completed.
Sub-saharan Africa (non tropical)
1. Green vervet monkey: A very common small monkey.
2. Grey-crowned crane: A pretty ground bird to spruce up shared habitats.
3. Black rhino: The last rhino for which we already have props.
4. Grevy zebra: A second zebra species. The Grevy is the largest and has thin stripes.
5. South African giraffe: A second giraffe species. This one has a very different range from the reticulated giraffe and has different spots.
6. Dikdik: A tiny antelope species.
7. Giant eland: A giant antelope species.
Sub Sahara Africa is very full already, but I would make these couple of additions to make it truly complete.
USA
1. Raccoon: The well-known trashpanda.
2. Skunk: This little striped icon needs to be included.
3. Bighorn sheep: Another sheep from North America, but I think this one definitely has a place here.
Just these couple of animals would make the USA complete.
Canada and Alaska
1. Musk ox: This large ungulate is the only extra addition I would make.
Together with the wolverine, there are now plenty of animals to turn this area blue.
Mexico
1. Collared peccary: A drylands-dwelling pig-like creature.
2. Nine-banded armadillo: A common armadillo species.
Together with the
ocelot, howler, spider monkey, coati, manatee, kinkajou, and
sloth, Mexico will be complete.
Central America
Central America has such a high density of animals, that it is far from complete representation right now.
1. Ocelot: The spotty cat from South and Central America.
2. Howler monkey: Central America needs more monkeys. The first one is the Howler monkey.
3. Spider monkey: The athletic spider monkey.
4. White-nosed coatimundi: The widely requested coati.
5. West Indian manatee: Can't go without a manatee for representing this area!
6. Hoffmann's two-toed sloth: Not sure if this animal could work in-game, but a sloth is very popular.
7. Kinkajou: A cute small arboreal animal.
Tropical South America
This region needs more fleshing out, particularly with more monkeys.
1. Squirrel monkey: South America needs more monkeys, so here you go.
2. Bald uakari: A funny-looking red-faced monkey.
3. White-footed saki: A light-colored saki monkey species.
4. Red titi monkey: A titi monkey species.
5. Scarlet ibis: A dark red-colored ibis, because we don't have a South American ground bird yet.
6. Marsh deer: A slender marsh deer species.
7. Bush dog: A small canine species.
Patagonia and Pampas
1. Maned wolf: The first animal that comes to mind.
2. Patagonian mara: A unique small rodent that kind of looks like a small antelope.
3. Viscacha: A cute fluffy rodent.
4. Darwin's fox: A fluffy dark grey fox species.
5. Vicuña: A wild version of the domesticated alpaca.
Can't build for this region right now, but together with the pudu and the Andean cat, these animals will complete Patagonia and the Pampas.
Andes
The Vicuña and Viscacha count for the Andes as well and will complete this region along with the following animals.
1. Southern pudu: The tiniest deer species in the world.
2. Spectacled bear: South America's bear species that lives in the cloud forests.
3. Andean cat: A small pretty wild cat species. It kind of looks like a miniature snow leopard.
Australia
Australia needs quite a few more species.
1. Red-necked wallaby: Australia needs wallabies. This one is very common.
2. Yellow-footed rock wallaby: And another wallaby species, smaller, more colorful, and with a smaller range.
3. Wombat: Australia's not complete without a wombat.
4. Eastern grey kangaroo: Kangaroo variety, and greys are more commonly found in zoos outside of Australia I think.
5. Emu: Australia's not complete without the emu.
6. Tasmanian devil: The icon from Tasmania.
Non-Australia
1. Matschie's / Goodfellow's tree kangaroo: Either one is great.
2. Kiwi: The bird from New Zealand.
3. Coconut crab: A giant land crab.
4. Eastern long-beaked echidna: An echidna species from New Guinea.
5. Little blue penguin: a pretty little penguin species.
Along with the cassowary, these species I feel represent non-Australia completely.
Antarctica
Looking for more penguins here, and for a penguin predator.
1. Leopard seal: The penguin hunter. A large and fearsome seal species.
2. Macaroni penguin: The well-known crested penguin.
3. Adelie penguin: A smaller classic black & white penguin.
As usual, doing this took way and way too long.

Hope you enjoy.