Taken from www.reefkeeping.com

Gramma brasiliensis, the Brazilian Gramma, is extremely similar to Gramma loreto. The only notable differences are their origin and a few minor cosmetic differences. Gramma brasiliensis is only found in Brazil, and visual differences occur in the jaw line, dorsal fin, and their slightly different coloration. Gramma brasiliensis' jaw line extends slightly past the pupil, and the first dorsal spine is noticeably shorter than the rest of the spines. Brazilians violet is not as intense as G. loreto, and the fade from violet to yellow is more gradual.
The above is taken from www.reefkeeping.com Pictured left is the brazilian Gamma and Royal Gamma on the right.