I am making a 3 colored butter cake for a little girls party.
How do you all caLL this cake?
Rainbow cake?

Rainbow sounds good. Confetti cake?

I think rainbow sounds better. When I hear confetti, I think of a white cake with multi-colored specks in it rather than a swirled cake.

Hey that's it, Rainbow Swirl!

http://www.wilton.com/recipes/recipesandprojects/Easter/scrambledcolors.cfm

this link from wilton is for their scrambled colors. They give you ideas/instructions on how to color your cake batter/effects.

on a lighter side:
depending on what colors you mix, the color could be called, rainbow, multicolored, or puke if you are not careful

just kidding, but good luck!

I was trying to think of the punchline I was about to read while I waited for it to load. Slightly disappointed this was a serious question!

I've heard others refer to it as a ribbon cake.

If the colors are really bright you could call it jewel-tone cake, or bejeweled, but I guess that sounds like they might expect to find diamonds in the cake.

Crayon-colored?
Twisty cake?
Marble cake?
Yeah, rainbow is also good.

Grey? Or at least that's what the parti-colored cake I tried to make with the kids "HELP" turned out to be. Parti-colored refers to something of more than two colors, in the cake sense it could carry a double meaning...

Rainbow Swirl!!

I made a rainbow- colored cake for my next door neighbor. It was decorated with smiley faces on top. To this day, (probably 8 years later) those kids call it "Face Cake" because it had smiley faces on top! So we have done Face cake decorated many different ways over the years... I thought that was cute!