Colour blindness is not limited to a few colour combinations. There are many subtle rarer forms which most people either never notice, or rarely appear in the information or natural world.
Computer charting displaying multiple data sets can expose difficulty in recognising rarer forms. It is for this reason that typically "poster colours" are preferable over mere shades, and if possible other distinguishing features such as shading. Arts and Media crowd love to pick similar shades which can make distinction difficult on certain displays.
Cheapest TN panel displays only display 6-bit colour, and fool the idea into seeing (say) a shade of green. Viewing that colour in peripheral vision and it can appear yellow to most people (the display is using interstitial colour mapping to create a colour it can not naturally generate by being limited to 6-bit). Classic being the Thinkpad battery life bar, and it is particularly annoying to some people.
Many companies buy PVA or IPS monitors, which can display 8-bit colour. So a confounding factor can indeed be the display is junk :-) For me the worst problem was always with greys, and particularly sharp text (I find reading fuzzy inkjet easier than ultra sharp laser).