Dark grout Stephen Webb 27 May 2013 14:28 EDT

Hey All, Looked at a porcelain tile floor, customer said she had it
cleaned and when the guy finished the grout was dark and he said it
would dry the proper color (lighter) it didn't and when I tested it I
couldn't  get any results. I noticed a hard color change in the closet
where his cleaner stained it and where it was light and clean. What
could cause the color to go dark? Strong Acid?