I think I've been successful in the past by boiling some water with high concentrate RIT die (i.e. the whole box) - turning off the burner and the popping in the parts for an hour or two. The result isn't a heavy color though, and mostly a dark tint of color.
I think that's my next experiment. For this one, I think I'm gonna soak it cold one more time, maybe another time, and then use it for a while to see how it wears/ages. The deeper the color the more preferable for me, however even a medium grey is good. I'm not a bright or vivid colors kinda person.
I think that using Rit diluted for silicone isn't worth trying unless you want an extremely light tint. that's why I decided on full "strength"
I have 3 more white ones to dye plus about 8 light grey ones I can test on. I also have a yellow one.

The vinegar was a light purple color and now the sleeve is about half as dark as it was initially after my last soak in the dye. But that's OK, it's still a lot better than white.