I'm sorry I can't be more specific. I'm going from memory from a photo that I saw. It just struck me as being quite striking! I know it would help a lot if I could give you a geographic region, but I'm afraid I can't. The picture that I have in my head is of a slim snake, small headed, with red and yellow bands. And, yes, there may have been some black, but not much. And I can't really say for sure if the bands encircled the whole body or not.....but I think so.
:No other colors? That doesn't ring a bell. But there are a LOT of colubrids in the world, the vast majority of which aren't found in the pet trade. It might have been an elapid, too.