The crafting recipe to dye wool only appears when using white wool as a source. Even the recipe for white wool (wool + bonemeal) is available only if you are already starting with white wool!
Dyeing sheep from any color to any color seems to work fine.
Comments 2
Logged new issue ( MCPE-8907 ) to address minor waste of bonemeal issue.
OK. It seems confusing that there is a recipe: wool + bonemeal, when this can only be used to make no change whatsoever. I tested it, and it will gladly waste your bonemeal. Perhaps this recipe should be removed.