Food coloring is water soluble, Having dyed 100,000's beads and wood chucks making parrot chew toys for cage birds when the item gets wet the color runs.
Rit dye is also a water soluble dye that is salt based. You can use it the hotter the water and the longer in the bath will deepen color of some colors. Again depending on the wood or material foam rubber you may have to rinse the excess color off to keep it form staining hands or other things.
Rit dye is also not listed as a food safe colorant if kiddies may put it in their mouth.
Check out WC or Rockler or Lee Valley for real wood coloring dye. well worth the expense and you can get the mixed coloring in bottle and just add fresh colorant as needed. Works great with alcohol, and some works with water.
S-P-F and hard wood beads food coloring
Rit dye tan color clown cowboy hat
On the food coloring follow the ole grama's using vinegar with the coloring and water for easter eggs it can make a difference, but the smell may linger.
:clown: