It could be a coincidental result of the fact that primates have unusually good colour vision, or a side effect of having evolved from animals which displayed rainbow-coloured patches to indicate sexual availability.  But it's also true tjhat many flowers are edible, and they tend to come out in spring when there isn't much else available.

European hedgehogs often anoint themselves with strong-smelling substances, chewing them up and then spreading the scented sailiva over their backs.  This presumably has a practical purpose - probably to disguise their scent from both predators and prey.  But I have found that they seem to derive pleasure from shoving their faces into strong-smelling herbs and snorting about in them, even if they aren't going to use them to self-anoint with.