Lol I had one do the exact same thing before. She only faded on the edges of her fins and no where else. Kinda gave her a neat outline. Her sister on the other hand seemed to do the exact opposite, had her entire body fade except for the edges of her fins.
+1, basically all that gene does is remove most, if not all, of the darker pigments from the skin leaving behind only the brighter colors. Here's an example of a fader vs a normal RD. Both are Red Dragons but 1 has the fader gene while the other did not. Major difference in color to say the least, granted mine faded almost completely. P.s. this is a father and daughter pair, the mother had the fader gene but didn't show much of it.