I have the same thing! I have 2 false perc and the smaller one is beginning to turn darker. At first I thought it was due to the lighting in the store was different from my lighting. I feed it the same pellets my LFS
said they use so I don't think its the food.
I just went and took a closer look my smaller clown and the possibility of it being a true perc seems highly possible now. I chose it specifically because of its thicker black lines, but the lines seem to be fading a bit now.