I bought a purple iMac USB keyboard, because I thought the lovely
translucent plastic was just crying out for some internal lighting.
Opening the case was difficult, in the end I had to break the six plastic tags holding the top of the case on (they're at the front). But it glued back down fine afterwards.
There was loads of space for the side LED's (where I cheated and used 5V LEDs rather than solder in a resistor), but the center (blue) LED only just barely fit under the Apple logo after gently dremelling away the plastic from the cable grommet.