Note: This may require you taking apart your RD. I do not suggest you do this if you do not know what you are doing/don't want to void your warranty.
After having the blue LED display now for awhile I decided maybe it was time for a color change. I changed mine to green as it's easier on my eyes at night while driving.
What you will need:
a bag of plastic colored hanging folder tabs (wal-mart etc.)
Now you can can choose whichever color you want but just remember it's blue + [color of tab] = [final color]
Now you can do this without taking apart the RD by just taping the final result to the front of the RD.
First take out the color you want to use, test it by holding it up to the RD while it is on to see what color result you will get. Cut it so that you end up with something like below:
Now if you're doing this by placing it on the INSIDE of the RD you will need to unscrew the bottom screws, now be careful as MEM-TEK has warned you about static discharge, do this in a "safe" environment to prevent you from zapping your RD by mistake.
Once the bottom part is taken off, I'm not too sure on the 78 but on the 73 the front led cover should just pop up with a little bit of work and should come off easy (calling MEM-TEK for input on this!)
Now once you have the front cover off simply slide the plastic in place making sure it's nice and snug (should be a snug fit and hold in place) and then simply replace the cover and put your RD back together!
End results daytime/night:
Now if you're looking to stealth out your 78 then pick a red tab. This will make your display blacked out and then you would only have audio warnings. Of course I don't suggest doing that but hey if that's what ya want that's one way of doing it.