Make sure they are not using watered down grout, which will dilute the cement content, weaken the mix, and wash out color. The grout should be paste-like and not soupy. Another tip recommended by most grout manufacturers is to dry mix all bags of grout together before mixing with water to get a consistent color throughout the entire job. Also, make sure they are using two 5-gallon buckets at a time (instead of 3.5 gallon), one for initial wash, and one for clean rinsing. These buckets need to be changed out often. Finally, if they are buffing the haze off with towels, be sure they don’t scratch the grout surface, which can cause it to dry with streaks.

If this continues to be a problem, you may want to try a more color safe grout. A couple of good ones for color consistency are C-Cure Cureperfect 930 and Mapei UltraColor.

Good luck!