Does anyone know if you are supposed to use a special ribbon for cakes so this does not happen? The only reply I've received is to put a strip of wax paper behind the ribbon. Anyone have any other ideas?

double the ribbon if possible with a white ribbon slightly wider than the colour one you are showing. That way the colour ribbon doesn't touch the cake at all.

You should test the ribbon 1st on a piece of the icing you are using, lay it over the icing on a small saucer or plate over night to see if it bleeds, not all ribbon colours bleed.

HTH

A lot of CCers use wax paper. I don't and I've never had a prolem with my ribbon.

I read somewhere to back the ribbon with that clear tape you put on packages to ship. Clear, not the kind with thread in it. I did this and it seemed to work great. I had to trim the tape to make it the same width as the ribbon before I put it on the cake.
j.