Better question is why are we still holding on to red and green at all?
10% of the male population can't tell the difference, especially if the shades are close or lighting conditions not optimal.
F***ed if I can tell the difference between L/R nav lights of an aircraft at night!
Even had to tell Shagpile off for a feature he added for the next OzRunways, telling him to change green to yellow so I could tell the bloody difference between on and off.
Some industries are catching up and some manufacturers are better than others. A few years ago, Olympus changed the single status LED on their chargers to red/blue. No I can tell the difference between charging and finished!