i wouldnt. maybe a heather gray.

If you DO decide to change the color of the brick, although this isn't my area of expertise, let me suggest that you use a ceramic stain, rather than an actual paint. Reason being that with a ceramic stain, it would give the appearance of the brick actually being that color, rather than being painted.

I would leave it as is, just put a round mirror with a black frame above the fireplace to tie it all together.

Gee, I have the same color on my walls and VERY ugly brick fireplace. I am now tempted to paint it black. Your rug is grey? I agree with the heather grey since I can see some that color in the rug. Is the chair grey-ish? even more of a reason.

The carpet is pale blue and will eventually be replaced. The area rug background is a nice gray. The sofa and ottoman (which shows in the pic) are medium gray (Pottery Barn and Crate and Barrel both have the same gray denim slipcovers).

Creative ceramic and tile--gave good advice ! Also the link you provide shows what appears to be natural gray or stained gray brick--not painted brick, also the color is a goon medium gray, I would not go darker than that.

You have a lot going on in this room. But I would not paint FP gray. The white is fine. I would change out mirror over FP to a much bigger picture. Something with your wall color in it. tone down all the things on mantel. And bookcase.

I would remove area rug. Rug over carpet will discolor your carpet over time. You have enough busy, keep it simple.