I'm a big believer in pre-washing anyway, especially if I'm going to give the project to someone.
Like Juliasb, I have certain colors I am always more concerned about than others. My own quilt that was ruined by a badly dyed piece of fabric was maroon. I know blues often have a lot of excess dyes and they are actually the ones I worry/test most.
And, I have had red dye "crock" that is transfer over from one piece of flannel to another. I had bought both pieces in a bag from the thrift store, one solid bright red traditional flannel, the other a white background Christmas flannel and the red transferred onto the white. So yes, I would definitely wash with a color catcher and dry fairly hot and if I'm not going to get around to a particular piece in a timely fashion, I wrap it in tissue paper before putting it in with other fabrics.
Even though I don't like to work with flannel because of the amount of pet hair in my household, I did a quilt last year with a flannel back and it came out lovely. Still don't want to want to work with fabrics, but they have their uses and advantages.