Spectacular quilt!
After it's quilted, when you do wash it using Synthrapol, be aware that you *must* use lots of water with the Synthrapol so any dye bleeds become very diluted. Also be aware that the quilt should be continually agitated; you do not want wet red fabric in contact with white fabric for any period of time. What I like to do is use the largest front loader at the laundromat for washing with Synthrapol. It uses enough water. The quilt needs to be removed immediately from the washer when done and either put into the dryer right away, or laid out flat to dry.
Although Synthrapol requires hot water to be completely effective, it is still pretty effective in warm water and even cold water. Since you already washed the red fabric several times, it should be fine to use warm or cold water with the Synthrapol.
Would love to see a photo of your quilt after the quilting is done!