Oxi-Clean powder made into a paste with some water can help with the white grout. Try in a spot and make sure it doesn't cause the floor to be too slick. I used it on tile walls and it worked very well. Just apply the paste with your finger and let it dry a little before scrubbing with a small brush to see how it works in your situation. (I used it on glazed tile, not tumbled marble.) If the grout is moldy, try Tilex Spray for Mold Removal. It works fast and does a great job. I also swear by baking soda and water for some stubborn stains. Hope this helps.

Wow...angry much, that might be one of the most rude replies I have ever seen! If you don't like others posts, seek life elsewhere!!

I took the advice of a few folks on this garden forum and tried out finazzle and it worked!! We were in the process of selling out 11 years old house and needed to re-grout our kitchen tiles. It was originally off-white and after 11 years it turned to a dirty brown color. Finazzle made it look like the orginal color. Of course, you have to use a little bit of elbow grease, but it came off fairly easy. The only bad thing is that you can only order it on-line and I think the minimum order is $19.95, and it includes free shipping. Good luck! Jenny

If the grout joint has a consistent height around the tub of 3/4", and alternative to a huge caulk joint could be to use something like a tile trim or liner piece to fill most of the gap. There are certainly restrictions going that route, ie, there might not be a proper material in the back of the gap to bond the liner to. If you do go the "all caulk route", look at backer rod as millworkman suggested. Backer rod is a foam rope that comes in different diameters. Backer rod gets stuffed into the gap to act as a filler for the deepest part of the gap. It greatly improves the performance of caulks when they are used in large- or deep-gap situations, as a large slug of caulk. If you filled a large gap with a single large slug of caulk, as the caulk cures and shrinks, internal shrinkage can cause the caulk to pull away from the edges, or even crack in the middle of the joint. Backer rod allows a Thicker depth of caulk at the edges where you need adhesion, and a thinner depth of caulk in the middle of the joint where you need flexibility.