I have dyed tone-on-tone (white) with procion dyes. As "I Love to Quilt" says regarding designs, the little sprigs of flower buds did not dye. This was the effect that I wanted so all was good. That said, the design was more muted compared to an undyed sample and wasn't stark against the now lavender coloured background. I would do a test before committing a whole lot of fabric.
HettyB