Quite a lot of people are colour blind and have poor colour discrimination. There are tests that can be carried out and these include the Ishihara test (which is a screening test that I certainly remember from School) and the Munsell 100-hue test (where people have to arrange a number of coloured discs in order). These tests need to be performed whilst being viewed in daylight. There are online tests but these are less reliable – partly because the viewing conditions vary such a lot. I recently came across a new online test provide by X-rite. It seems to be based on the 100-hue test (or, at least, something similar) and I can see how it could work, despite being an on-line test). I just had a go. It gave me a score of 34 and suggested that for my age group (and gender) the best score was 0 (perfect colour acuity) and the worst was 99 (low colour acuity). Hmmmmmmmmm. I have a version of the 100-hue test and I can perform it perfectly. My real score should be 0. I have perfect colour discrimination. So, much as I like the X-rite test, I have not changed my opinion that on-line tests like these should be used for fun and should be understood to not provide an accurate assessment of your colour vision. On the other hand, it could just be bitter because I only scored 34. 🙁