It's a thing called Patina. See the link below for more info on why Vachetta leather changes color.I have artsy mm mono and never have a problem but my concerned how can I taking care of my artsy..like changing color of the shoulder leather..could u pls help me or any way to avoid dis coloring the shoulder strap ?? Thanks everyone
I hope this helps

>Vachetta FAQs
>Patina FAQs