Depends how colour blind they are...
I knew someone once who saw blue as red....meaning that the sky looked like blood red to them. They were a Chemsitry Teacher too :p.
My Dad's colourblind and he sees red and green as the same colour and can't tell subtleties in shades. My mum has to pick out all his outfits or he would always clash. I've inherited it slightly so for example if I watch snooker I can't tell the brown ball from the red ones and I have trouble with petrol blue tones.
i just can't imagine what it would be like to see one colour where another one exists in reality.
if you see one colour, how would you describe that colour?
There's a webpage www.vischeck.com (sorry, dunno how to put it in blue and make it a link - I'm a computer moron) that will let you change your page to the different types of colour deficiencies, so you can see what a person with the problem actually sees.
in the late fifties when i was at school we were tested for color blindness it was pages full of coloured dots and you had to suss out what number it was . which i failed completely ,am i colour blind ??havent got a clue??
apart from the dot test, how do you know a colour blind person is not seeing the right colour, as we grow up we are told oranges are orange apples or green or red, a colour blind person may see blue but they are taught the colour is orange, green red etc
i think that we know that what we see is blue because that is the answer agreed with by the majority of people. it's the fact that so many people see the same thing that makes it 'reality'.