The colors are so dark and intense. I did the shirt in diagonal stripes, in rainbow order. It came out quite well.
Dry dyes are dangerous to inhale, and spread through the air easily.
Dyes that have been dissolved in water are much safer. When working with powdered dyes, always wear a face mask. This one is easy. You get to skip making the dyes dissolve, a step which always takes me an hour or two since I can never seem to resist making big batches. This technique, in which dry Procyon dye powder is sprinkled on soda-soaked fabric, results in very intense colors and an interesting pointilistic effect.