MargenBeavers' teeth are a deep orange, and not for lack of hygiene.
Their enamel is reinforced with iron, the same metal as tools, and that gives them that rusty colour… and an extraordinary hardness, able to gnaw through whole trunks without wearing down. What's more, their incisors never stop growing: which is why they need to gnaw constantly to keep them in check.
A chainsaw made of teeth, powered by iron, that sharpens itself.