I have been searching around the internet for ideas for examples they could go for this kind of concept for various species. Maybe they could do this for each of the species. Whatever the case, I think it would be best if they stuck with one "exotic" skin per dinosaur species. The examples I'm going to show are stuff that could fit well with the theme Frontier are going for this game of theirs. They've confirmed a long time ago their dino skins are purposefully designed to look like they would belong in the series (particularly, without explicitly saying this, from what I've seen, the film series), with the help and guidance of Universal Pictures themselves. So, here's some details I'm gonna share that could fit with this goal of theirs regarding dinosaur skins.
The first one bellow is based on a cut, but reasonable design from the production of one of the movies.
1.
Pteranodon (model change): The
Pteranodons from the JP DLC all have the same model, including the ones based on the ones from
The Lost World: Jurassic Park, which used a slight different model on-screen. However, there was a piece of concept art for these pterosaurs that closely resembled the questionable genus,
Geosternbergia. Although the design never made it to the final film for the pterosaurs, the exact design was still carried over to two subsequent Lost World games. There is no current positive consensus that both genuses are synonyms, since the pterosaurs with this design are supposed to represent
Pteranodons in the games, and that all the ptero skins in-game are based on only one model, this I think could be a good way to add an "exotic skin" with a model change to the JP DLC Pteranodons in-game. It is, again, concept art that didn't make it on-screen, by the way.
The remaining eight bellow are designs are stuff from various places, including other JP franchise games. Now, because of this, they would be unable to legally copy and paste these designs I'm sharing as examples. Instead, they are just for reference to kinda build from for their own designs, as long as they stay within Frontier's confirmed goal for dino skins as mentioned above.
2.
Acrocanthosaurus (no model change): Some dinosaurs, like the
Acrocanthosaurus, have two alternate skins that differ in both pattern design and color intensity. To make an "exotic skin" feel more special to them, how about have a skin that is a mix in between? One where the new and unique eye-catching patterns are much around the body and the colors around it aren't always too dull or too intense. Something like the
Acrocanthosaurus from
Jurassic Park: Operation Genesis for example bellow.
3.
Stegosaurus (no model change): Some dinosaurs, like the
Stegosaurus, have only plain body patterns, outside of their plates. Having an "exotic skin" to have an eye catching pattern on the main body would be one perfect way to do so. For
Stegosaurus in particular, many people who know the franchise will remember it as a green colored dinosaur, so why not something interesting in that color league like this image bellow from one of the few pieces of merchandise for
Jurassic Park?
4.
Maisaura (no model change): There are some dinosaurs in-game that have only one pattern for all of their skins, rather than two in their skin categories. The
Maiasaura, for instance, has a very stripped pattern going across their bodies. To balance things out to make things more special looking, maybe have an "exotic skin" where the
Maiasaura has no heavily patterned body. Either no pattern at all, like in this image of a museum model of one bellow, or at least keep the heavy pattern to not only a great difference, but to a very low minimum.
5.
Ouranosaurus (no model change): Some dinosaurs have exclusively plain patterned skins all around, such as the
Ouranosaurus. To add life and uniqueness to them, perhaps a more standing out detail would be nice.
However, I wouldn't recommend anything too crazy looking for them. An
Ouranosaurus "exotix skin" would probably still be kept grounded to its style in-game, but with a balanced touch of detail on them somewhere, something like the
Ouranosaurs from the 2011 BBC documentary,
Planet Dinosaur, for instance.
6.
Spinosaurus (no model change): For some species with only one pattern that is heavily detailed, they don't have to become duller for an "exotic gene", they can an alternative detailed looking skin with a unique look in both pattern shape and colors. The
Spinosaurus I believe can be one of them, and here's an example from the game,
Warpath: Jurassic Park that you can unlock on survival mode.
7.
Indoraptor (no model change): Some dinosaurs are mostly very dark. In particular, the
Indoraptor is always black in the general sense. So, like the black Indominus rex further above in another comment, an "exotic skin" for the
Indoraptor could perhaps be white in color instead. There is concept art of a "
second Indorraptor" to be pale white in color that didn't make it pass concept for
Jurassic World: Fallen Kingdom for reference.
8.
Spinoraptor (model change): What I like about hybrid dinosaurs in general is that you can come up with various designs per type. For the ones that appeared on-screen, I believe have a lesser chance for such concept here. But, the ones that didn't, which were the hybrids introduced in the Dr. Wu DLC, I think have a much better chance. The
Spinoraptor in particular can have a unique "exotic skin" design with a less pronounced sail and a head that is a little more spinosaurid-like, something like this piece of art I found from DeviantArt, by user
Tapwing.
9.
Triceratops (model change): Ceratopsians in general I believe have a chance for a change in frill and/or horn shape, as long as they are kept grounded enough to represent what species they are supposed to be. The image bellow from the handheld game,
Jurassic Park III: Park Builder, I admit is probably way too over the top for this game. But the idea should still be pointed out for an "exotic skin" for the
Triceratops, where it's horns can have a slight curve effect and maybe being a little bit extended (not as much for the nasal horn as shown bellow), kind inspired by how rhino individuals can have different shaped horns. At the same time, should have a skin that is unique (but not too crazy looking) from the rest of the default skins.
but mixing a Stegosaur and triceratops together maybe just can't give good results... triceratops and ankylosaurus maybe? Triceratops and kentrosaurus? Ankylosaurus and kentrosaurus? 
i dunno, hybrids aren't really that interesting to me.. maybe if they mix a Suchumimus with a quetzalcoatlus and make it unable to fly but looking really really strange? Hmmmm... still nope... I want realistic dinosaurs xD
