Heat (at least the temps generated by a domestic dryer) does not permanently set most modern dyes, so I would not consider that a problem.
Most likely the dye transfer occurred because you used cold water with Synthrapol. The purpose of Synthrapol is to suspend unset dye particles (like the ones that settled in your yellow fabric) in the water so they are rinsed away instead of settling into fabric. Using cold water made the Synthrapol unable to do its job.
Honestly, at this point I wouldn't worry about it. I would finish the top, *then* wash with Synthrapol and lots of hot water in a large washing machine. The dye particles that settled into the yellow are not permanently set, so they should lift out and be rinsed away. You might have to wash two or three times this way to get all of the dye bleeds out, but they will come out.
For Synthrapol to be effective, you need both hot water and lots of water. By any chance, did you wash the top in a front loading washing machine? Most domestic front-loaders do not use enough water for Synthrapol to be effective. In addition to hot water, you want *lots* of water so any dye bleeds are thoroughly diluted.
Keep in mind the same thing would have happened if you had washed the finished quilt in cold water instead of just the top.
Last edited by Prism99; 07-14-2014 at 01:12 PM.