One practice of game developers that sometimes annoys players is repetitive use of creature models. Art assets cost time and money. To stretch their value, developers sometimes apply a new color scheme and new stats to an old model, and voila! a new creature! It's not just a goblin now. No, it's a water goblin!
Well, with a little guidance from God's own handiwork, this method can be made more acceptable to players and perhaps augment gameplay at the same time.
Nature is full of encoded color schemes. Provided a game doesn't provide labels over the heads of its creatures like EQ, variations in color schemes can be used to reward player knowledge and create more depthful gameworlds.
One of the more famous models of real mimicry is the kingsnake/milksnake, which has a striped pattern very similar to that of the coral snake, only with the colors arranged in different order. ("Red on yellow kills a fellow. Red on black, ok Jack", if I remember right). The kingsnake's bite is harmless, but the coral snake is venemous. Thus, two possible mix-ups are if a person avoids the harmless snake for mistaking its color for the venemous snake, or a person might mistake the venemous snake for the harmless one and get into a peck of trouble.
Applying this situation to a game, players could be encouraged to develop an awareness of the gameworld's natural trickery (or paying for a companion with such knowledge) and opportunities are created for interesting encounters. Applied merely to unintelligent creatures, the player might get unwarranted scares or make deadly mistakes, like with the snake example above. Applied to intelligent beings, like a humanoid race, differences in appearance could inform players of community differences (it's the economy-focused Albek tribe, not the war-mongering Magori) which affect gameplay.
These differences could be more than just "threatening/non-threatening". They could inform the player of the best approach to different ends (Tribe A is susceptible to intimidation, Tribe B to bribery, Tribe C to foreign jewelry or weapons, etc). The coloration of some insects and amphibians informs birds that they taste disgusting or cause vomiting/sickness in some other way. Likewise, different colored species of one creature model in a game might inform the player that its hide produces poor tailoring results, that it cannot be eaten, or that this particular species can climb trees.
There may be any number of situational clues. An animal's rank among its pack/herd/whatever may be signified by its color pattern. Maybe taking out the leader first causes the others to flee or lose leadership buffs. Some species may be loners, others typically found in small groups, while others typically found in large groups. If a game allowed members of a creature group to dynamically stray short distances from one another, then coloration could add to the player's strategic repertoire by giving the knowledgeable players a means of determining how many allies a target creature is likely to have nearby. Coloration and size may denote the creature's sex, signifying dynamics such as aggressiveness... never mess with a mother guarding her young. =) With humanoids, apparel may signify profession...and thereby threat level, persuasion avenues, etc.
And then there's the obvious use of coloration: camouflage. I have yet to experience an encounter in any game in which camouflage made a creature difficult to detect or pinpoint while moving. Camouflage has many purposes in the real world, one of which is to make it difficult for viewers to focus on and determine the true shape of an animal. Translucent enemies in a few FPS games (ex: Halo) have demonstrated the fun than can be derived from enemies difficult to track.
There are countless opportunities available through stuff already modeled in the real world like this. This is just the tip of the iceberg. Another branch of nature modeling is stuff like a rattlesnake's rattles and the growling of dogs...tension-building warning systems.
Writers are commonly advised to write about what they know, a philosophy which has proven extremely effective for generations. The same advice applies to game developers. The natural world is limitless in models and lessons for environment and character design.