Ken -
While I have to say Enhancer Pro is a great product, I also know it doesn't do magic tricks either

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If the uneven color of the grout has been there since the grout was applied, the Enhancer Pro will not even out the color. Enhancer Pro will enhance
all the colors and the grout will still be uneven, just richer in color....The Enhancer has no way to be selective.
Might have been a grout clean-up issue..... if too much water is used during the wipe back, over worked wet areas will have the cement, additives and sometimes the color powder rise to the surface causing a difference in color in those areas. Try scratching through it or scraping off the top layer... See if the correct color grout is just below the lighter areas ...