How to clean rubber strap?

[Bork99]

I bought my wife a Chopard Happy Sports ceramic rep with a white rubber strap. She loves the watch and has been wearing it daily since she got it a week or so ago, but over the weekend wore it with a new red coat, resulting in some red marks on the strap edges.

I've tried the typically recommended soap and water and alcohol, with some fairly brisk rubbing to try and get the colour out but no luck. I'm worried stronger chemicals wll damage the rubber, but at this point it's either that or I need to resort to ordering a new strap anyway!

Any one with any cleaning tips/advice? (Other than "don't buy white rubber straps" )

Thanks!