I think all that is would be an extra red light added to come on when you key the mic, there is no color change. I thought you were talking about the meter lights that cycle from green, yellow,orange, red, blue, and so on.
You could probably check out an old Galaxy 99 or Magnum S9 and see what parts they add.
Most of the old Realistic Navajo bases had this feature. Check the schematic for a TRC-458 to see how it's done. Pretty simple really.
-399
Here is what I'm talking bout.
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