I dyed a pack recently, and thought I had gotten all the stain out. Well, a day of hiking in the rain showed otherwise. The purplish dye leached into the rear of my new Ex-Officio light khaki pants. (That's them in my avatar) After washing them they were bright pink. I finally messed around with some dye and got them to a light brown color, but it still has a touch of pink...looks like granite. :-) You could dye that RR shirt, but if it uses Polyester thread, the stitching color won't change, so take that into consideration on choice of colors.
What color leached out of the pack? Was it from black material or the blue pack body material?