I would choose a tile that has one of the colors of the stone, You could use a traditional stone tile, or use a modern contemporary wood grained tile.

I would go with a tile the color of the lightest stones with maybe a touch of the tan color - not too much. Cool mosaic!

THANKS EVERYONE FOR THE ADVISE. WILL POST PICS ONCE BATHROOM IS REMODELED.

Please turn off "caps lock". It's hard to read posts in all caps.