I'll take a slab at it. Maybe a buttercup? I have three that I bought from a local hatchery and they look just like yours and they were sold to me as buttercup.
I don't know why my previous post didn't go through. So here it is again. I think the only thing you really need to be worried about is the plastic melting and getting on your chicks. The ignition tempature for rubber ranges from 260°-316°. So I don't really see a heat lamp getting that hot. IMHO
We had a set up similar to your and I had 6 checks in it. The heat lamp was fine as long as it wasn't within an inch or so of the plastic container because it melted the handle off. The ignition tempature of a rubber bin is anywhere from 260°-316°. It will melt at a much lower temp...