sounds like you have a fabric that may run when washed- if the color is coming off while it is dry. i have had this happen once- with a red i was using and really (thought) was stable. i had ran water through it and believed it to not run..then while sewing noticed the edges of my machine had red on them- when i washed the quilt i used cold water and threw in 3 color catchers- and all 3 were bright red when they came out- along with the whole quilt being quite a (surprising) shade of pink.
i have forced my self to be much better about pre=washing