Are you talking about the toyota factory stereo?
Was wondering the same thing too....I have a factory stereo in mine as well, hooked up to a JL audio clean sweep, and I wanted to see if i could change out the LED's to white bulbs.... so I took off the face, and it turns out that they're tiny green LED's soldered onto the circuit board. I'm sure it can be done, but it's not a plug n play simple job.
I'm planning to go with white LED's, but because of the green lights on the stereo, I'm probably going to leave all my HVAC controls green, and just change out the lights on the guage cluster.