Yes, we have all had this experience, most often from efflorescence. The best one I know of that dries very uniform is CurePerfect 930 by C-Cure. It has a white powder base with a separate liquid colorant that is added rather than water.
Another excellent choice is UltraColor and UltraColor Plus fast drying grout by Mapei. It is supposed to by efflorescence-free. Good luck!
Michael Prachniak - Expert Tile and Stone Consultant and Writer, Owner - Tile Productions
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