I dyed a few for DS using a kit. Then I just dyed a few more last week for my DD on the way. You want the fiber reactive dye whether its from a kit/box whatever. What this means is you need the kind that requires the multiple steps of either soaking/adding soda ash and usually also urea in addition to the dye. Rainbow Rock was the brand I found at Michaels, they also sell the kits there but you do NOT want the "one-step" kind as that is the equivilent to RIT which I hear will fade a lot after repeated washing.
My learning from last week... if you want pastel colors use a TON of water and way less time than required on the box! I wanted a nice soft purple so I used 4-5 times the water it called for and only soaked for 5 hrs vs 24. They are Vikings purple right now- very, very purple.
I also learned that even with shipping its cheaper to order through Dharma than in the store. I just ordered on Tuesday and got my shipping notice today (Wednesday) so their turn around is definately good enough for me. Plus, they have tons more colors to choose from.
If/when you do yours pls post pics as I'd love to see!! I'll be posting mine once I get them all done. I just ordered 3 more colors from Dharma in add'n to the purple ones I already did... so I'll have a rainbow of colors to show!
I used Rainbow Rock dye for my prefolds. They turned out really pretty. I wish someone would have told me how to do it at first because I was really lost. I would buy extra soda ash. The prefolds absorb a LOT of the liquid, even after you kind of wring them by hand. After doing about 15 prefolds, I didn't really have much soda ash and water left to soak more than 1 diaper at a time.
I used dylon and did them in my kitchen sink. It was easy, took about an hour, and I only needed salt for extra ingredients. They turned out very pretty, and I made sure to wash them several times to rinse out the extra dye. (And I did colors that I would be ok with if they were not SUPER bright, because I did not know how the process would work.)
After it all, my prefolds are super cute, still soft and snuggly and my daughter LOVES to get to pick the color of her diaper (we only have white BSWW for covers.)