From YPPedia

Monkeys are one of the four familiars types which can be found on the oceans. Monkeys come only in their respective natural colors, as seen below, and thus are available in fewer colors than parrots or octopi.

The familiar palette shows the colors available for player-owned familiars.

Historical Note

It was once possible (in Azure) to obtain monkeys of other colors, such as navy, pink, or even black. The photos of Duncan and Ursela's wedding show several such monkeys.