Dunno if anyone's mentioned this, but for rubber parts like flex bottoms plastidip works really well. Main advantage is you can turn any color into any other color (provided the color of plastidip you want exists).
Tried dying a Vios frame and facemask black (from Purple)... 2 hrs in the mixture of 2 bottles/ 3 gal hot water (just below boiling), and not even a hint of color change.
Gave up, rinsed off, and dried overnight. Looks like I never even attempted it.