My colour vision is poor - a career in air traffic control was shattered at the age of 9 when I couldn’t read any of the numbers in those arrangements of coloured blobs. However, I have never had any difficulty with OS maps, any scale. In fact I prefer how they look to the sample “colourblind-friendly” map on the OS website.
As a colourblind person, I have learned over the years to recognise the colours that I see and know what colours they are supposed to be! In effect, the only remaining difficulty is selecting a tasteful combination of suit, shirt and tie in a morning, something that students and colleagues will confirm remains a difficulty!
As for the supposed difficulty interpreting traffic lights mentioned on the OS site, this is complete rubbish. Even if a person’s colourblindness was so extreme that they couldn’t distinguish between bright red, amber and green, they would still have little difficulty in determining top, middle and bottom!