Once had a debate for a good 5 minutes over an ink colour before he came clean and confessed he was "a bit" colour blind. He went on to tell me he distinguished stop lights by the lights position on the pole—not by the colour, because he couldn't tell them apart. He had difficulty with reds, greens & similar.
At another large shop owners jumped at an introductory reduced rate to convert all lighting to using less power consumption. Didn't need to be a genius to foretell how that would work out.
Sure enough; before too long word came down that several customers had mentioned their colours not matching correctly.
Owners insisted that the power company had informed them that the amount of light was identical to before the conversion (and they stood by that), when a moron could clearly see that it wasn't.