Coloring is a code word for
sex as used in the movie Sex In The City. When you don't want someone or a group of someones to know you're talking about
sex, or if you're in a public place where the word is not acceptable,
sex is referred to as "coloring".
ERIC: Kamron I
got all dress up and made you this nice dinner because you
said there would be coloring tonight!
KAMRON: I'm not in the mood for coloring. I have a headache.