Your darker colors can as shown in bearisgray run when washed. You can take a small square of fabric and pretest it. Place it in a small container, add hot water with your detergent and shake it on and off for about 10 minutes. Rinse and put on a white paper towels. I never prewash my fabrics unless I know I have a runner. With color catchers, I just don't worry about it. I live in an apt complex and it just takes too long to press out all the fabric. JMO.