Stained plimsolls after washing. Solutions?

[MNetcurtains]

Reposting here for traffic.

Popped a pair of plimsolls in the washing machine yesterday, all good, but as they're drying yellow stains are appearing. Any advice as how to remedy this/ prevent it happening in the future?

Put them outside in the sun?

Plimsoll whitener on Amazon or from a shoe shop. Just paint on the canvas. It covers grass stains etc.

I'm overseas and they were in the (very warm) sun. I'm wondering if that's part of the problem.🤔

Thanks, I'll see if I can find some.