Hrm.. I have seen them before. It looks like a color morph of the C.corona green version, or it could be a C.flavovirens morph. I've seen the striping of the corona that way but it has spots like the flavo which I haven't seen in corona.
I'm wondering what these are as well, though I've always thought of it as C. corona. Mine seem rather horny, I always find them bonking each other's badonkadonks.