Had a problem once with poorly mixed dark grout. It came out hazy. We painted it the color we wanted with a regular enamel, but this was for a very small area and it does not get foot traffic (a mantle for a gas stove). It worked, but was tedious. Now, I know you can get special grout stain or grout paint. Never used it, but my tile supplier is confident in its performance, and I trust his word. Check with a tile store. I think you may get a better quality product there vs. at a DIY warehouse. Don't despair...you have easy fix options.