Originally Posted by ardinos

One good reason, the plastic itself is green.

When I do a HID leveling switch or intercooler sprayer switch, the piece of plastic that the light shines through I pop out. I then take and very carefully use a Qtip and non-acetone nail polish to rub off the printed/ painted (not sure which) coloring on the back of the plastic. Done right you have a plastic piece which is now clear and just shines with the color of the bulb or LED behind it.

For the knobs for the HVAC, the plastic itself is green, there is no coloring on the backside, it's tinted green throughout.

What this means is in order to shine red, you need to only shine red light through the plastic. If you have any green wavelenghts of light coming throught the knob, you'd get green and red which is I forget what color, but it's not red. (Being an amateur astronomer I should know this, damn.)

Anyways it can't be done, trust me I checked and there is no way to remove the green color from the knob itself, hence red LED's.