Observations that he himself had made persuaded Goethe to reject Newto
n's theory of light and to put forward an alternative theory of the co
lour phenomena seen with a prism. Duck has argued that Goethe's attack
on Newton's theory rested on valid experimental observations that app
eared to present a difficulty for Newton's theory but to support his o
wn views on colour. Duck has also proposed that these observations may
be accounted for as an instance of the Bezold-Brucke phenomenon. It i
s argued here that this explanation is invalid and that two other feat
ures of colour processing can explain Goethe's observations.