I do wash my fabric. The worst colour run was a bright pink from a very well known quilter/designer. I soak any fabric I think may run in very hot water. Let the water cool then rinse and soak again in very hot water. After that I let it dry completely (line dry) then iron. I find this sets the colour. If fabric only runs a little at the start I'll soak in hot water only once. I find the complete dry and ironing seems to work.