I think some colors of RIT have always sucked for plastics. I dyed a Cherry set not too long ago with purple RIT and they turned out amazing. I am not sure if other people do it the same way as me, as I have my own 'tricks' for dye PBTs. I use a 6l stock pot, 3 liters of distilled water (this is important as most tap water have too much mineral and trace materials which can cause spotting/streaks), 500ml white vinegar (acidity helps with dye absorption), and the entire dye packet. I use a wire basket with handles to put the caps in, this way I can quickly and easily pull ALL the keycaps out to check color and stop dye at same time for best even color. The other thing that is very important is temperature. You want to keep it at 180-200°C so use a thermometer. It's best to have a high temp to allow for best dye saturation since it 'opens up' the porous material, but you also need to make sure it's not too hot where it starts edging into the PBT melting point where the key begins to deform. When it's time to stop the dye, I have another pot or the sink full of ice cold water ready.
