If you already have the white snowflakes attached, there isn't a whole lot you can do to guarantee no bleeding when washed. Synthrapol in the wash water is supposed to suspend loose dye in the water but it needs to be used with hot water.
I would make a red and snowflake quilted block and give it a try in the wash. If it is a disaster even with the Synthrapol and colour catchers, I wouldn't waste any more time on the quilt. Wish I had better advice but some fabrics never stop bleeding or crocking.