is it possible to do a red velvet cake in rainbow colours? are there any alternatives to making a black cream cheese frosting without tons of cocoa powder? boyfriend's birthday is in 90 days and i'm horrified!!! 

Black cream cheese... that's a new one.  The alternative is tons of black food color that will stain everyone's teeth - not a great look unless there's a zombie theme or something.

Yes, it's possible to make velvet cakes in any color, but you would probably want to leave the cocoa out to get truer colors.

Isn't the whole point of red velvet that it is, well, red?  :-s

Make the frosting (not the RV cake) in rainbow colors.

Use black as an accessory/trim/decorations frosting, not all black frosting.  Example:  Black roses, leaves, writing, ruffles, borders.

I've make velevet cakes in all kinds of colors so yes you can definitely make it a rainbow inside. The cream cheese frosting might change flavor though with all that black food coloring. 

How about a black velvet cake with rainbow colored icing as filling?  

Here is a recipe I found for black velvet (although I am sure any red velvet recipe could easily be adapted to suit whatever color you wish)

http://iambaker.net/black-velvet-cake/

may I heed one small warning regarding heavily colored cakes....you may want to warn the consumers of said dyed cake that their potty color *may* be altered significantly from the dye in the cake. (I get that it isn't exactly the best thing to lead with when talking up your cake)   I only say this because I once made blue velvet, and I had a small panic attack the following day while changing my lil ones diaper when it revealed a very vibrantly colored, smelly suprise.   I had totally forgotten that kiddo ate a piece of blue velvet cake...now I know to not be alarmed.

It works better for dark colors to airbrush the buttercream. Then you don't have to add tons of food color that will stain everyone's teeth and tongue and .....

thanks for the prompt reply everyone :) is it also possible to do whiskey cream cheese?