While in Louisiana we used a company called Grout-works. They did a wonderful job cleaning, painting, and sealing the grout. It looked like new and you could change the color as well. I credit them with selling our house since the grout looked so bad before they did their magic. After they finished you could pour red wine on the grout and leave it sit for an hour and it would wipe off with ease. They have locations near TV. Use the link below.
Tile Grout Cleaning, Color Sealing, Repair, Shower Restoration