Interesting, the other colours are all references to real things, I think. Blue mould; purple-faced (lilac) angry people; green of (say) a diseased limb, or as we describe someone's face when they're vomitous.
So, what is "hot pink": Hot metal before it's red hot? A blushed person's skin??
So, what is "hot pink": Hot metal before it's red hot? A blushed person's skin??