Prism99

I would simply test all the colored fabrics to see if they are colorfast. Drop a small piece (maybe 2 inches square) in a clear glass of water and wait a few hours to see if any dye bleeds into the water. After that, rub the still-damp fabric on a piece of each light-colored fabric to see if any dye transfers that way. (Not all light fabrics pick up all dyes, so even if a dark is not absolutely colorfast it may not be a problem if the white you use does not pick it up.)

If a fabric does not pass the colorfast test, I would wash that fabric in Retayne (which permanently sets dyes) and re-test. A few fabrics require two passes with Retayne. Any fabric that is not colorfast after two washings in Retayne should not be used in a quilt.

Color transfer is what I would worry about. Shrinkage is typically not a problem, so it doesn't matter if some fabrics are washed and some are not. Once the top is quilted, it is the batting that determines shrinkage. IOW, a fabric will not shrink more than the batting will allow. Any slight differences in shrinkage among fabrics will be unnoticeable in the quilt. (This does not work if the quilt is tied, or if quilting lines are very far apart. In those cases, there is enough space for a shrinkage-prone fabric to shrink to its max.)

After the quilt is finished, make the first wash one with Synthrapol. Synthrapol suspends any unset dye particles in water so they do not settle in other fabrics.

Both Synthrapol and Retayne need to be used in *hot* water. Synthrapol requires a lot of hot water in order to keep dye particles adequately diluted. For that reason, it is not recommended for use in domestic front-loading washers (which do not use enough water for the Synthrapol to be effective).