Red–green colour blindness affects up to 8% of males and 0.5% of females of Northern European descent. Colours of traffic lights are confusing to these people as there is insufficient apparent difference between them.

To avoid discriminating against red-green colour blind people, suggest adding textual status to avoid confusion:

Another approach

Maybe use blink rates? Not as clear - the user has to know what the blink rates mean - but once they know they can remember forever. Might also help those without colour blindness too.

• No blinking (steady) on Green
• Slow blinking on Yellow
• Fast blinking on Red