I've tried to bleach out the sun tan on pieces of vegtan where part of the hide had been exposed to sun while stored. Used oxalic acid at varying strengths, up to a really strong mixture where no more crystals would dissolve. It doesn't bleach out!
Some of the marks from what I can see looks like the natural wrinkles in the hide. They look good and as said, are natural. Again, you won't be able to get rid of them either.