Whether you get a seed after sleeping, and whether that seed is a hybrid, is random, so depending on how long you played, it may just be bad luck. (I know that when I was play testing it, it seemed to take forever to produce purple cosmos specifically...but I couldn't find any reason for it, and an acquaintance who play tested it seemed to get plenty of them. I assumed it was just the RNG being finicky.) Additionally, red and yellow don't produce a hybrid.
Still, I'll look into it and make sure it's behaving properly before I upload the post-jam update.