Having thought on this for a while, one group of animals that I think have a lot of options for added diversity from reskins would be exhibit animals. These are six species that would be particularly simple, as all are in the same genus as an animal already in-game and would require only a new skin:
Golfodulcean poison frog: Derived from the golden poison frog (both in the genus Phyllobates); is a vulnerable species endemic to Costa Rica that is very different in colouration to either poison frog currently in-game and widely kept in captivity (at least 62 zoos in Europe alone).
Strawberry poison frog: Derived from the Lehmann's poison frog (both in the genus Oophaga); a Least Concern species from Central America that is very familiar and frequent in captivity; although there are 15-30 natural colour morphs, the most famous and the one included here would be the 'blue-jeans' morph.
Beaded lizard: Derived from the Gila monster (both in the genus Heloderma); looks very similar to the Gila monster externally, but it has a different colour scheme and lives in tropical rainforests in Mexico; they are also kept in captivity quite frequently - these would be based on the Rio Fuerte subspecies.
Lemur leaf frog: Derived from the red eyed tree frog (both in the genus Agalychnis); requires changes in body and eye colour but otherwise little difference; they are Critically Endangered, found in Central America and Colombia and are part of a captive breeding programme in European zoos.
Aruba rattlesnake: Derived from the western diamondback (both in the genus Crotalus); this would need the biggest change, being quite a bit smaller than the current rattlesnake but it represents a Critically Endangered species of snake and would be the first arid exhibit species from South America.
Ethiopian mountain adder: Derived from the puff adder (both in the genus Bitis); this species looks almost identical to the puff adder except for its bold green-and-black pattern; they would use the tropical exhibit and are kept and bred in zoos, albeit not in huge numbers.
