Blue, purple, pink, and crimson [red] appear [to me as] ... all referable to blue. I have often seriously asked a person whether a flower was blue or pink, but was generally considered to be in jest. Notwithstanding this, I was never convinced of a peculiarity in my vision.
- John Dalton, Memoirs of the Manchester Literary and Philosophical Society, 1798.
(In French, color blindness is called Le Daltonisme in honor of his discovery of the condition.)