Badger, welcome.

It seems like you might appreciate some more details. The ;light; is actually just coming from the back of the display panel. Apple have simply cut an Apple shaped hole in the display rear housing to allow light through. As mentioned this can be tinted effectively with gel, I see no reason you couldn't print a colour transparency to do the job if you want more than one colour.
Like Jacob says, all you need to do is cut the desired shape out of the lid.

Care must be taken when removing the rear housing, there are two screws in the bottom front corners, the rest is done very carefully with a putty knife or similar.
Its easy to scratch or crack a display doing this so really take your time.
There are some electronics and labels on the rear of the LCD panel. These are arranged so that they avoid the apple logo on the back. You will need to bear them in mind when designing your logo.

I am not aware of anyone producing blank rear housings that would fit. Possibly you could have one fabricated but expect to pay a fair bit for it.