24 THE WAY OF A TROUT WITH A FLY 



VII 

 THE SENSE OF COLOUR 



I. A Query. 



So many who have argued in print on the subject of the 

 colour-sense of trout have argued as if there were only two 

 possible alternatives — namely, that trout must see colour 

 as mankind see it, or else must be wholly colour-blind. 

 I venture to suggest that that attitude of mind takes too 

 little account of the wonderful variety of nature. It might 

 well prove to be the case that, without being colour-blind, 

 trout are more sensitive to some colours than to others, 

 or they might be wholly colour-blind to one primary colour 

 and keenly sensitive to others. 



A person completely colour-blind sees all objects in a 

 neutral grey, the form and reflected light alone distinguishing 

 one from another. 



A simple way of illustrating what I mean is to take 

 things in their simplest form. There are three primary 

 colours — violet, red, and green. All other colours are a 

 combination in varying proportions of two or more of 

 them. The simple combination of any two of them makes 

 the complementary colours. Sensations of different colour 

 are produced by rays of light of differing wave-lengths. 

 Now assume, for the sake of argument, that trout are 

 sensitive to red only, and colour-blind to violet and green. 

 Then a combined colour made up equally of violet and red 

 would look to him precisely like a combined colour made 

 up of red and green in equal proportions, for his eye would 

 only accept the wave-lengths to which it was sensitive 

 and reject the rest, thus selecting that part of the combined 

 colour to which it was sensitive, and rejecting that part 



