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I was recently asked to replace a dual-color LED in a TC Electronics Ditto Looper pedal. The person requesting the change has a variation of color blindness that prevents him from distinguishing red from green, and those are the two colors in the Ditto's LED. I chickened out pretty quickly, though, and never even opened the Ditto to look. I didn't feel like frying something and being stuck with $130 non-working pedal. Instead I came up with a solution that did not risk any damage to the pedal and did not affect the pedal's value or warranty.
I had some 3-D glasses on hand (Red and Blue) and cut the lenses out. I cut two little squares—one of each color—and stuck them side-by-side on a piece of tape. I placed the tape over the LED so that the line between red and blue was right in the middle of the LED. Green would have been a better choice than blue, obviously, but I went with what I had on hand, and this seems to work well as is.
Because the red lens makes the red LED brighter and the green darker than it would be ordinarily, and the blue lens makes the red darker and green brighter, when the LED is red, the left half of the lens lights up. When the LED is green, the right half lights up.
There are surely countless ways to make this solution look better, but this quick, cheap and easy solution works in a pinch.