What Porsche said.
The fact that you can see what you think of as green and what you think of as blue as distinct shades alone means that you're distinguishing between them, which many people can't.
My eldest brother has red/green colour blindness, which meant he couldn't join the RAF as he planned.
( Malchick, Mon 29 Jun 2009, 18:00, archived)

There used to be a rule in football in that
if it started to snow while the game was being played, they would change the white ball for a orange one, as the orange ball showed up nicely against the white snow.
However, if the snow melted during play, they were not allowed to change the orange ball back for a white one, and this caused problems for players with colour blindness as the orange and green are two of the colours that cause problems for colour blind people.
I suspect the rule has changed now.
( turb0t, Mon 29 Jun 2009, 18:05, archived)