People tend to assume that colour blindness, or colour vision deficiency, is an on-off thing - that you just see grey, or that all colour blind people have the condition to the same degree. Mine is fairly mild, I maintain – it reveals itself in poorly lit shops where I pick out grey clothes and see they are labelled green (no, not lime green, but perhaps a dark olive or almost grey kind of green). And I am slower at picking raspberries than other people – I see the red against the green leaves but they just don't sing out to me as they obviously do to others.
Around 8% of men and 0.5% of women have some degree of colour blindness, mostly red-green. It is apparently genetic and carried by women, not men (somewhat ironic then to hear mothers criticising their sons' choice of clothes).
I found these christmas cracker facts on a useful website called colorblindor, run by Daniel Flück. It has a lot of resources and links – I was especially gratified to find his online RGB Anomaloscope test which reports on your degree of colour blindness (Ishihara just says you are or are not). Although all online tests are accompanied by a health warning about monitor settings, it seemed to work for me.
One useful feature is this colour vision deficiency simulator. You can upload an image and see what it looks like to someone with various colour deficiencies.
