We had the tile replaced in our shower. Everything was removed (tile, wallboard, etc.), and new tile was installed. Some small areas of the grout are darker than others. About 90 percent of the grout is the desired beige color. A number of small sections are a brown color, as if the grout didn't dry. The contractor used polyblend sanded grout. The darker coloring is especially bad in the corners of the two niches for holding soap and shampoo bottles. See the attached pictures.
What caused the problem?
How can we get rid of the dark sections of grout?
In the future, how can this coloring problem be prevented?
The grout was applied Monday, October 12. The contractor let it sit 48 hours, and was going to seal it October 15, but he didn't because of the color problem. So the grout has been untouched since it was applied a week ago.