Coming from a coloured blind person, (red/green) I find that BLUE is a huge problem. I have no idea why. I can see both red and green but they are very hard for me to differentiate. Yellow is probably best for visibility at distance. However, blue is one of my favorite LED colours as long as I am close to the display. The other three colours are good if I am near by, and red is probably best for distance. However, that said, if you are using red and green to show different states, red/blue would most likely be the better choice, at least for me.
I hate the single, dual colour leds used on almost everything these days as I can’t tell the difference between the red/green, green/yellow, and red/green/orange leds.
Clint Millett, Calgary