Look at your picture, Kris, the water is beading up on the disc. DX and Pro are particularly hydrophobic and Rit is a 'direct dye' that is 'water-soluble' and, hence, has a problem with getting into the plastic. In reality, the actual dye never goes into a true solution because the color is carried as small particles caught between groups of water molecules and is never really solubilized. Adding acetone to the water helps 'open' the plastic by loosening the polymerized chains enough to allow the particles of color to become lodged in between (much like in fabric, which is what Rit was really designed for). Increasing your acetone concentration can get you better results, but even though acetone is miscible in water, it will still evaporate out of the solution as it is heated. It can be hard to tell just from the smell if there is still some in the water because the smell of the vapors will linger in the air, and the nose, for a while after it is gone from the solution. That's why people get different results with DX. But, putting in too much acetone can have adverse affects on the plastic, and subsequently the shape, of the disc.
I once traded someone a Pro Beast for a Pro monster and wanted to remove the sharpie marker scribbling doodle dye job that was on the top, ('monster' face)
and it wouldn't all come off with isoproponol. So, after wiping the hell out of it acetone, I put it in a gallon ziploc (which are impervious to acetone) and then filled it with acetone and left for a few minutes. No change. After checking on it several times over a few hours, I decided to leave it in overnight. Bad idea. By morning, the flight plate had expanded, while the rim had not, making the disc look like a giant bottle cap!
It was freaky lookin'. The disc 'dried out' after about a week and the flight plate actually shrank and changed the overall angle of attack on the wing of the disc such that it flew unpredictably...beyond understable. Nothing like a Monster.
The other way to get better results with Rit, is to actually grind it up farther with a mortar and pestle, but this requires gloves, a mask, a high quality porcelain mortar and pestle, and patience because it must be done slowly so as not to make a big cloud of dust. In other words...not recommended.
Rit also has to be in a slightly alkaline or neutral solution, never acidic, and always near boiling point, to work. Rit also contains salt to help attract the dye particles to organic fibers. Boiling down an acidic salt solution, increasing its concentration, and then leaving it in the pot and heating it up again is going to break down the metal.