I only had to do something like that once, I had a clock radio with a bright yellow LED that was pointed right at my head when I was asleep. It was the FM stereo indicator, and it stayed on all the time, no matter if the radio was on or off. Turned out the radio was always on, but the audio amp was turned on and off by the alarm. I got out my box of old LEDs and put the dimmest red one I could find in the hole, and then put some of this blue sealant I had over it, and it made a nice dim purple light.