Re: useless for the colour blind, who use the layout of the lights
To be fair to the previous poster, they *may* be well-versed in the various different types of CVD, and were specifically thinking about the small percentage of CVD people who genuinely do have no colour vision at all, rather than the far larger percentage who merely suffer from some degree of deficiency.
Or, as is more likely the case, maybe they're simply part of that surprisingly large group of non-CVD people who really do believe that colour "blindness" is a binary condition rather than the far more complex spectrum it actually is.
Like you, I don't have any difficulty with things like traffic lights that some people automatically assume I'd struggle with as soon as they find out I'm red-green deficient. My favourite example of where I really do struggle comes courtesy of our Samsung fridge freezer, which has a built in water/ice dispenser and accompanying filter cartridge. On the door there's a small LCD to show the temperatures, dispenser settings etc., and also whether or not the filter needs replacing. Most of the LCD consists of blue on black characters/symbols, however when the filter has expired the symbol for the filter changes to red. Being merely red-green deficient as opposed to completely unable to see red, this isn't the problem.
What *is* the problem is that, in the weeks leading up to the expiry of the filter, the symbol first changes colour from blue to purple (I'm assuming here that Samsung decided not to splash out on a different backlight LED here, and are simply driving both the blue and red ones). However, the only reason I know it changes to purple is because my wife asked me one day what the purple light on the fridge meant - to my CVD-afflicted eyes there's no discernable difference in shade between this symbol when it switches between blue and purple, even though the shade of red used is, on its own, quite distinct.