Stone veneer. You can stain it or paint it.

Most time it is referred to as "fieldstone". It may well be just a veneer over concrete block. If it's a veneer it wouldn't be incredibly difficult to remove it and put a different material back. Looking at your hearth I tend to think it is a veneer.

Oops! Just reread your post and you aren't looking to have it removed. I agree with painting or staining it.

I can only mind the dog. That's a great dog.

Looks veneer. You can paint it pretty easily. How do you want it to look?

HI -- I like the river stone/field stone . If you paint it or color wash it , it will make it look dead and uninteresting. Get a new fire screen or heat paint that one and then do another mantel that looks more driftwood . What I really do not like is the wood wall - that is what is dated looking ... so either remove it for some ship lap or reclaimed wood or paint it a weathered grey . This will give you a modern up dated beach look .