I usually prewash my fabrics. Reds and very dark colors are especially bad about colors running in the wash. Shrinkage is not such a big deal with me; but I do panic when I seen a color faded onto the light colors. That said, I just finished a redwork quilt top. When I put the blocks together, I spritzed them with Mary's Ellen's Best Press as I pressed the top. The red embroidery thread ran on two of the blocks before I realized what was going on. Next time I am going to dip the finished blocks in a vinegar water to set the color before I press them. Live and learn.