You want to use fabrics that are colorfast in your quilt. If the dye in a fabric runs when you wash it, your whole quilt could be ruined. I recommend washing all your fabrics before you begin (or at least soaking them in warm water to see if they run). If you notice color in the washing/soaking water then the fabric dye is not colorfast. Sometimes you can correct this by placing the fabric and 2 cupfuls of white vinegar into a sink full of hot water. After about 30 minutes rinse the fabric. Place the fabric into a sink of warm water and see if any dye is released. If the fabric continues to ‘bleed’ (release dye) then don’t use it in your project.