Black foam is white/yellow foam that has been dyed.
You would not see it for Kitchen supply because the dye can rinse out and the dyes are pretty nasty in addition to coloring all your pots and pans and ****.
You would not see it for craft supply because the foam is commonly entombed in a pillow or cushion, and even slight dye bleeding would wreck that, in addition to the fact that nobody will ever see it.
Whats wrong with yellow foam? The 5'th best headphones ever made by sennheiser* (HD414) have bright yellow foam pads...
Make a name for yourself. Its not a failure, its a feature!
*Only sort of joking. They are really good, considering when they were made. Ignoring when they were made they are actually pretty nice.