In reply to M6PEW:
You’re the 1st RG colour blind person I’ve come across who can’t tell the difference on LEDs. I’ve worked with several RG blind electronics engineers over the years who never had a difficulty telling the difference between red and green LEDs. Colour bands on resistors were a problem for them but that is solved with a DVM. (Must get a new high voltage battery for my AVO8 if they are still made.)
The only problem they all had was setting the brightness of red displays. Due to their reduced red sensitivity they tend to set red displays far too bright for people with normal RG vision. It was a case of “is this too bright?” where the reply would be “yes”. Adjustment of the series resistors was needed. In fact the RG people I know used the dullness of red objects as they saw them as a big hint that the item was probably red.
So normally the brighness change is the giveaway when the led changes colour. As Mark says a red filter will attenuate other coloured light than red and the same for green filter. AS long as you know which filter is which you can tell the colour of the LED if the brightness is not enough.
Whilst you are one of 283million men with colour blindness that’s only 1 in 12 of the world male population and that does not make up the majority! Neither does it make your condition particularly rare. My daughter’s chromosome translocation makes her 1 of about 10000 in the world, that’s quite rare.