When people from different races have sex, calling it rainbow sex, because of all the different skin colours there are.
A dark person, a fair person, a caucasion person and a mixed person have an orgy, it is called rainbow sex
de superhungarishman 6 avril 2010
When a group of girls wear different colored lipstick and suck a guys dick, leaving different colored rings on the dick. Creating a rainbow effect :)
Me and 4 chicks had rainbow sex last night! RED YELLOW GREEN AND BLUE!
de Shwanky240 13 juillet 2009