Menstural Cup Icky??

Hey everyone, I’ve been using my menstural cup for maybe a little less than a year now, and I was wondering if there’s any way to get the brown coloring off so that it’s back to it’s white self?

I know that it’s clean, because I boil before and after every period and I’ve even done H2O2 soaks and tried scrubbing it down with a washcloth but nothing really seems to get it all off. It was fine and white for the first few cycles, and I love it dearly, but it’s kind of embarassing.

I bought it specifically for the convinience, cleanliness and environmental sustainability and it basically being immortal, but that all gets washed away if I have to buy a new one. Any suggestions or anyone who’s delt with this before? Thanks!