I have used a powered product called grout colorant.
There is a liquid colorant called Tints-all.
And you can always water down some acrylic paint and
do a wash.
I have to rush to work so I can't give you any links,
but you can always google or search on ebay!
Hope this helps.

no one can ask a dumb question here, never happened before and never will!

Cindiloo is right, you can get powered cement colorants. Tints all is a pigment used to color paint.
Some have good luck adding acrylic paint to their grout or waiting to do a color wash over the cured grout. in both those instances you'd really want to be changing a close shade of the same color family.
Stll other members have used rit dye to color grouts...

I have heard of people also using chalk to tint grout also, like the sidewalk chalk kids use. Use the small grater on your cheese grater.
Natasha687

Thanks for the help. I can't wait to start a project using a colored grout.

Maybe some of my friends could buy different colored tints and swap off. This would give us all different colors.

Your tile store in your town should have grout in many colors. I might add here that one mosaic artist told me that Tints-all is the only colorant that w/not fade outside. All others will eventually.

Thanks
My daughter bought a house with a big bunch of bags of white grout so I think I'll buy the tint and work with the "tints all".

carolann_z8 -- do you mean to re-color grout? If so, I am in the process of using Aqua Mix Colorant and Sealant. I'm mixing 2 colors. You can purchase sample sizes to test areas and then order the color/colors you like. It's actually fun and the results are excellent. Let me know if this is the sort of thing you're looking for and I'll post more info. I've been helped so much by these forums--I wanted to share my experience.

I'd like to know where you're ordering it, Stargaret. Thanks!