On a related note, this can also be done to dye the rubber part of grillz (if you have the white set)
I've experimented this morning with an old set of profilers and i3's, The profilers took on a slight hint of the colour as did the i3's faceplate. So I imagine you can do subtle colour changes on those but not major ones.
The clear lense frame of the i3's has gone a nice transulcent dark green. (and the foam fell off)
It seems the proflexes are just made out of the right material for the dye to work on as this also works on flex 8's and flex 7's
If someone wants to donate old or broken flex parts, I will try out some of the other fade and masking techniques for the guide.