i always use retayne. i get it at dharma trading company. a little goes a long way. i think it works better than the color sheets. all the color catchers work the same way: they capture the loose dye.....hmmm... molecules? bits? in the water and allow them to be rinsed away. if you think you need something really stronger, then you can use synthropol, which is a color setter. this company sells both. they supply dye, dye removers and other chemicals related to dyes. the quality is very professional and can be trusted if you follow the directions.
http://www.dharmatrading.com/html/eng/1137-AA.shtml