I think for outside, painting it after you are done is the best way to go. It's easier than it sounds as the paint will wipe right off your tessarae and stay on the grout

Maria

I'm pretty sure they make a dark brown grout at HD.

So you are planning to use the adhesive as your grout also?
I'm not sure if the adhesive itself can be colored. You could just use the adhesive to stick your tessare to your hardiboard, then buy a colored grout to actually grout it with.

sassums,

I have colored Mapei Premixed Adhesive & Grout. For very light color grout, I have mixed in acrylic paint. For darker (meaning charcoal, dark gray, browns), I have used Rit fabric dry, the powder kind. It's difficult to color white grout dark with paint because you have to add A LOT of paint, and the grout gets too runny.

I have also painted grout after it's dried. That has worked best for black and gold.

Hope this is helpful.

Thanks for the help.

I'll do a small test batch, one with paint added, and the other painted over.