Epoxy is the most water resistant of all grouts and is probably one of the most durable, making it a good grout for a ceramic tile kitchen counter top where you will be scrubbing it clean all the time. But there are some tips for working with it.
It comes as a kit with three pouches: the A and B parts of the epoxy resin and a pouch of sand. Mix it exactly as it asks for on the package. Properly mixed it is very thick and a bit hard to work with, and it will get thicker fairly quickly as it begins to set up. Work with small batches and move systematically across the surface, completing the application as you go. Don't spread it all over and then come back to work it in. Because of its thick consistence you really have to work it into the joints. So work with a hard rubber spatula that allows you to push it in all directions to get the grout into the joints and the air bubbles out.
As with all epoxy mixes; you can slow down the setting process by working in a colder environment or even by putting your bucket of grout into a bucket of ice. If you are working on a hot day or have sunlight streaming through the window, epoxy grout will set up even faster than it says on the box; block out the sun.
YOU MUST WORK WITH A PARTNER
Once this grout dries, it will never come off of the tile face, so you must work with two people: one applying the grout, the other cleaning up right behind you. Right after the grout is spread out with a spatula, your partner can sponge off most of it. This will leave a film. Now you have to be careful. If you attack the film too soon, you will gouge the grout lines. If you wait too long, the film will be permanent. With a slightly damp sponge keep testing the film in the middle of the tiles to be sure it is still removable while you are testing the grout lines themselves with your finger to see when they gain a little solidity. At the right moment you can wipe off the film and polish off the joints without the grout in the joints catching up on your sponge. When the joints are really hard, you want to return with a sponge with clean water and keep cleaning until there is no film left as the tiles dry. Work hard now because no matter how hard you work later, it won't come off.
Epoxy grout is a lot more work to apply than regular grout, but it is just about maintenance free. And yes you can add grout colouring as you like. Just make sure that the colouring you use is appropriate for the grout you are using.