The shoulders of a piece have gone pale where the light hit it

Went to get a top out that I had not worn since the summer and the shoulders have gone visibly paler than the rest of it. It is a deep colour so the difference is very clear, and it follows exactly the line of where it was hanging.

I had it on a hanger on the back of the wardrobe door, and that door is roughly opposite a window. Nobody would call it direct sunlight, it is a north facing room, but it has clearly been getting light all summer.

Can this be brought back at all? And more usefully, is the rubber itself damaged or is this only the colour? I would rather know before I wear it somewhere and find out the hard way.