Getting the grout colour, you want has always been a struggle, as manufacturers tend to have a minimal colour pallet. Grout Colourant or powered pigment is another option that gives you a much larger colour pallet.
Grout colourant can be added to powdered grout. When using powdered pigment or grout colourants, add the powder to the dry white grout and mix before adding the water. Just remember that the colour will appear a few shades darker when wet.