This is a photo of my fireplace hearth before:

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I never liked the black and white tiles. I had them removed & now have replaced them with dark gray, large slate squares:

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They have not been grouted in, as yet.

What color grout would you recommend? The same as the old fireplace grout or a dark gray?

Thanks for your help!

P.S. The insulation hanging down was from an old fireplace glass door and will be removed. :)