I use my MacBook Pro for astronomy. The backlit keyboard would be great in the dark, but its white light is bad for night vision. This mod makes it red, or any other color you want.
This is a "unibody" MacBook Pro (17", early 2009). A similar procedure may work for other MacBooks. Assuming it works at all, that is: it may void your warranty, damage your machine, damage yourself, or damage your favorite stuffed animal.
The keyboard backlight is built in layers under the keyboard. Furthest from the keyboard is a sheet of plastic foil, white on one side and black on the other. A half-dozen white LEDs are mounted to this sheet. Next is a clear sheet with translucent white dots under the keys. The dots catch the light and redirect it up to the keyboard itself.
More details about the keyboard backlight construction.
To change the keyboard color, you need a keyboard-sized sheet of plastic between the clear sheet and the keyboard. It must be thin to fit inside the tightly-packed case, and it must be mostly transparent to avoid dimming the light too much. Note also that the inside of the case might get hot.
First, open the machine to expose the back side of the keyboard. This requires disassembling much of the machine. The iFixit teardown may be useful; I needed to remove the motherboard and DVD drive, but left the battery and hard disk in place and did not remove the fans from the motherboard.
Once the black sheet behind the keyboard is exposed, carefully peel it off. Don't tear it and don't forget which way it goes. Then peel off the clear sheet and cut your colorizer to the same size with the same mounting holes in the middle. Then put the keyboard back together - first the colorizer, then clear sheet, then opaque sheet - and reassemble the machine.