You can paint Corian, but why on earth would you want to paint over one of the best countertops available?

Refinish the Corian, please. So easy and inexpensive, even a beginner DIYer can do it without screwing it up.

Looks like two different materials. Do you have marble around the opening and on the floor? It will be cold to the touch.

If you have Corian for the yellowish mantle and uprights, you probably could paint that with the right primer.

The wood mantle surround is almost same yellow color as solid surface material, so it's difficult to differentiate, Ideally I would like to paint the wood AND the material around the firebox and floor hearth something very dark.

It really reads as a faux stone. But is definitely not real stone....it's man-made

Could be Corian Endura, that's more heat resistant. Are there any other places in the house with this surface?

I know old Corian can be painted, not sure about Endura.

You need to clean it, sand it very well (like with a belt sander), clean again, and use epoxy primer and paint.

Yes, this material was also used as bathroom vanity tops.

So, maybe this project used up the leftovers from the bathrooms. Can you peek around the edge and see if you can tell if there's anything behind the white surface? Maybe consistent with the inside of the fireplace?

It's cultured marble; not even close to Corian. It's disposable cheap junk and should be replaced.