I painted the three Castle Ravenloft board game Skeletons with slightly different colors (mostly on the shields and swords, but the bones have different levels of tints on them as well) so that people could say things like “I want to aim at the one with the blue shield!”.
The general approach for bones is to do shades of gray/white first, then tint them with a bright yellow wash, followed by a transparent dark brown (burnt umber) wash. Variations in lightness and color can be made by the lightness/darkness of the base coats, and amount of washes you use.