I am a rubber stamper....hence the name and I may be able to help you.
I was also thinking about doing this. I'm really new to CD expecting my 3rd in Feb and this will be my first time to CD. I'm not sure what kind of fabric bummis are made of, but there are some inks that are made especially for fabric. Fabrico---now called Versacraft is ink made especially for fabric. Memories usually works on most fabric if you heat set it. You could use any stamps...rubber stamps or the foam type ones. Bold stamps (solid image stamps) would be the easiest, or if you wanted to get really creative you could use regular stamps and actually color the pictures in...Versacraft ink also makes markers, or you could buy fabric markers from Hobby Lobby. Now that I think of it, I believe Hobby Lobby also sells some kind of fabric ink, I can't think of the name right now, but I've seen it near the dyes for tie dye and fabric paints. Hope that helps. If you have any more questions I'd be happy to help if I can.
I've heard of the nylon koolaid thing too. I bought some prowraps colors only they were out of the colors in the size I needed so I had to get white. But they are nylon so I'm also considering doing the koolaid dyeing thing. I did a search the other day on the diapering forum and read a little about it. I think I just searched for koolaid, but they had lots of threads about dyeing wool with koolaid and not that many about dyeing the nylon.
fabrico didn't work too well for me, i think b/c it is meant for natural fabrics, which bummi's aren't. i've had better results with craft paints and also with crafter's ink pads (not sure who the maker is, but you can get them in any of the craft stores. i cut some stamps with little all over swirlies and did a cover using them. i've also done "alphabet" covers and one using butterflies. lts of fun! just remember to let them dry for close to a week before using.
childishgoth....not sure if you are talking about the bummis or the prowraps colors but this is what the tag says on the prowraps:
100 % nylon outer shell
100% vinyl backed polyester lining
polyester gusset binding
nak-i did some proraps w/ a fabric paint called pebeo setacolor transparent. very cool stuff. i know michael's has it. you can get some very neat effects b/c it's sun sensitive-any shape you lay over the wet paint remains there if it's sun dried. you can also sprinkle salt on the wet paint and get a great mottled effect.
mama to DD She's a teenager! 12/19/97 and DS 09/18/03