If you’re not in the mood to remove all the old grout from your glass mosaic tile but you want a new color, you can actually change the color of the grout. But just be aware that professionals actually say it’s less work to remove the grout than to change the color.
The more porous the grout, the easier it will be to color. First you will need a grout brush, or even just a clean toothbrush, to apply the colorant. I hope you have a steady hand though because you definitely do not want to get the colorant on the tiles. Luckily most brands are easy to scrub off if you happen to get color on the tile. You will need to completely cover the grout, so be prepared for a tedious job ahead of you. Before you start applying the color, clean the grout very well because it will have a better chance of adhering to the grout.
The darker you want the color, the more layers you must apply. Allow the colorant to dry for at least 24 hours. Then scrub off any color that touched the glass subway tile. It sounds like a simple project, but it just takes a lot of time and patience to complete.