28 CONTROLLED NATURAL SELECTION 
be purposely conspicuous, as it cannot be 
indifferent. 
Yellow.—The primary colour, yellow, is a 
very rare environment for animals, and so it 
is very rarely used protectively. A few insects 
which fly in the autumn are yellow, in harmony 
with the yellow autumnal foliage. Sunlight 
penetrating young green foliage is not a pure 
colour but yellow-green ; this colour is found 
on the breasts of a number of birds, the 
Willow Wren (Phylloscopus trochilus) for in- 
stance; compare this with the yellow bar in 
the Goldfinch’s (Carduelis elegans) wing, and 
with the yellow of the male Golden Oriole. 
Red.— Above all others, animals coloured 
red are the most conspicuous in Nature, 
because it is never found in the surroundings. 
The rising and setting sun sometimes colours 
all things red, animals as well as their sur- 
roundings. Thayer is of opinion that some 
scarlet animals, Flamingoes (Phenicopterus 
ruber) for instance, are coloured thus to 
render them invisible against the red of the 
setting sun; that which has already been said 
about sky protections, under White and Blue, 
also applies to Red; a red animal against the 
setting sun, by contrast, looks not red but 
black. 
