I have used it before. I soaked a couple of pairs of faded black jeans for 2 days in a 5 gallon bucket. I would stir occasionally. I did not end up with streaks or splotches and they came out very nice, but the faded significantly after 5 or 6 washes.
I have not done it again, I did not think it was worth the effort!
Yep! That's Rit dye and what I explained in my last post above. Not worth the effort. No longevity. Not a single professional (or good hobbiest) fabric designer would use Rit for items they sell on Etsy or at craft fairs.
The only reason it is used in Project Runway is because it is sold at the Mood Store -- who sells bolts of fabric for
sewers, not textile surface designers, who truly
paint & dye fabrics for a living. And the projects in Project Runway are worn ONCE. No washing.
If the OP wants a list of blogs of real fabric designers who use the Setacolor paints I can give her about 20 blog links that I read consistently.
Here is one:
Jane Dunnewold, who wrote the book
Art Cloth, recommends it in her book & blog. she created an Art Cloth Challenge to her students & book readers. They all created art cloths, from blank white cloth and used Setacolor to create most of these art cloths:
http://artclothchallenge.blogspot.com/
Of course you can just dunk or paint your pants in ONE solid color.

Machine wash the pants - NO fabric softener - and while still damp, use a soft brush to lay on the color. Lay FLAT to dry, so there is no weird streaking or running. Turn over a few times to dry evenly. When you are sure no color will run, hang to dry. After completely dry, heatset with an iron or a few minutes. Done!