Today I experimented with Lumi Inkodye, a fabric dye that develops in the sun. Here's a sample pack of magenta on a square of cotton. I folded and scrunched it, then left it in the sun for ten minutes.
Here, the color starts to develop.
After developing, I immediately wash the fabric to remove the undeveloped dye. It's an interesting medium, but I think I'll leave it in the sun a bit longer to get a deeper color.