The product I use to paint grout is called Polyblend Grout Renew, and for this bathroom I used it in Snow White. I probably used of this bottle when I painted the tile grout, so a little goes a long way.
Design Sponge, Household DIY Project: How to Recolor your Grout
Finally Found a Way to Make My Grout Look Like New!!!
The 4-Step Guide to Renewing Grout (In Order of Increasing Grossness)
Polyblend Grout Renew Color Chart
A miracle grout paint product that seals as it stains, Polyblend Grout Renew is available in 40 colors -- MUST TRY!
How to Make Dirty Grout Look New
How to restore dirty tile grout! (Because crawling around on the bathroom floor with a toothbrush is my idea of fun!) May give this product a try if the cleaners don& do it.trying to find something that protects or seals worth a damn going forward
Custom Building Products Polyblend #333 Alabaster 8 fl. oz. Grout Renew Colorant