Well, I would say if you are going to wash a vacuum bag, and you don't want colors to bleed, hand wash in cold water with Woolite. I would imagine the detergent you use would cause some of the colors to leech from the fabric, so Woolite would prevent that since it's for washing delicate fabrics.
If you don't want to try handwashing it, the next thing you could do would be to blow the bag out with a vacuum with a blower port. Put your hose with a crevice tool on the blower port, and go to town on the bag outside. You could also try using a upholstery brush or a vacuum with a powered upholstery tool, or another hand vacuum.
