Examples from literature

• Any living creature exposed to the rays of a sun, which is certain to emit some chemical rays, is subject to coloration as a protection against those rays. 
• Of course copper would also yield a brown coloration, but I am supposing that the circumstances preclude the presence of copper. 
• This coloration of the milk is due to the growth of microscopic organisms. 
• We have always observed this acid reaction in the juices of plants with red or rose-red coloration, while the blue juices of plants have always exhibited an alkaline reaction. 
• When this condition is arrived at, an additional drop of nitric acid causes no dark coloration.