I would actually take a different approach and wash it in hot water with blue dawn dish detergent with a LOT of water. If you only have a front loading washer then do it in the bathtub. You can toss in the color catchers too. Dawn acts like Synthropol in that it suspends excess dye particles in the water so they don't bleed onto your other fabrics.
But this will only work for excess dye, if you have a true bleeder it will have the ability to bleed any time you wash the quilt so subsequent washes, even in cold water with color catchers could still result in a bleed onto the cream solid.
However the dawn treatment could effectively remove the bleed. Personally, if you have that many scraps of questionable trustworthyness, I would simply proceed and hope for the best. I would not gift the quilt though because the giftee will think they ruined it and feel horrible if it does bleed. Keep it for yourself and enjoy it and use it.