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2.
having sex with a girl on her rag
Hey I'm up for some rainbow sex. I don't mind.
by Sun May 10, 2006
 
1.
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!
by Shwanky240 July 13, 2009
 
3.
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
by superhungarishman April 06, 2010