Silicone Case Cleaning

Hello!

Six months ago, I purchased the Blue Colbalt iPhone 8/7 case. The case was perfect with the color spreading the whole case. Over time, I see the edges turn into a darken shade and lose the orginal lighter color. This has also begun in the middle of the case. Could this be because of movement for color loss when gaining friction upon taking it out of my pocket? Also, is there any way to eliminate these dark spots from the case.

(I have tried washing with dishsoap and rinsing.)

Thanks!