What color mortar?
The color of the thinset does NOT matter when installing anything except some marbles or translucent stones such as Onyx. You clean any thinset that oozes up as you set the tiles and go back to remove any you've missed. The top 2/3 of the tile thickness is for grout.
What you read should have read that you can "use white with light and gray with dark" with the thought that if a little shows, it won't be as noticeable. But that doesn't work either, white thinset is NOT like white grout, the same for grays.
Tile 4 You LLC Troy, MI
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