We put gas in, so now it should not burn dirty

Your design so far uses cool colors rather than warm ones. What about black slate for the fireplace? Or white brick, always sophisticated. Or add an industrial touch with a metal instead of brick or stone? I think a beautiful stainless steel or more rugged industrial metal look would be fab with your stainless steel kitchen appliances. And have a beautiful flow from kitchen to the room with the fireplace.

I agree with tile vs. brick for a more contemporary look. Assuming the yellow walls will be painted a light neutral, since the floors have quite a bit of variation, and since the kitchen has some gray, I would consider a relatively monochromatic neutral look for the fireplace.

Thank you for all the responses so far. My boyfriend really wants stone, (a geologist), plus, we already gave the mason a deposit. We have decided to go with a veneer. I'm not really partial to grey, but it seems to add the most warmth. Not just a color, but actual product info would be helpful.

It is a small house near the beach in Cardiff, so wanted a beach feel.