Thanks for the help!
Desjardin's Tang and Red Sea Sailfin (Zebrasoma desjardinii) are one in the same. However, the cheaper and more readily available Pacific Sailfin (Zebrasoma veliferum) is a little different. It is often difficult to tell the difference between these two when they are young. As adults, however, the Pacific Sailfin Tang retains its attractive juvenile appearance although becoming less yellow, while the Desjardin's Sailfin Tang will change stripes for spots and lightens in color.
Nope, adult Desjardin's definitely lighten up in color as they grow older.i think you've got the two of them switched? Desjardini's are the ones that are more vibrant and colorful as adults aren't they?