I was trying to clean the handle part. I thought it was color transfer from my jeans. But it got worse. So I started to experiment on the patch leather. It will turn darker if I use water, alcohol, soap water, vinegar, leather cleaner, and baby wipes. Oil, eraser, and corn starch won't help. I've tried everything I can to clean it. But it looks like a tribochromism. What should I do?