Many gemological laboratories grade both diamonds and colored stones, though some labs will specialize in only one or the other. The GIA and SSEF grade both colored stones and diamonds. AGS focuses only on diamond grading. Gübelin, a European gem lab, does both but is particularly renowned for its work on colored stones.  If you’re looking to have a colored gemstone evaluated, make sure you look through the services offered by the gem lab and see what sort of grading certificate they offer. GIA and SSEF both come highly recommended.