The colours in the child’s surroundings are important. They exercise quite a different influence upon a small child than upon an adult. Many people think that green has a calming effect upon children. But this is quite wrong. A fidgety child should be surrounded with red and a calm child with green or blue-green.
The effect of red upon the child is as follows: If you look upon a bright red and then turn your gaze away quickly to a piece of white paper you will see its complementary colour, which is green. … By this I mean to, illustrate the tendency which the eye has to produce the opposite colour. The child also attempts to do this; inwardly he seeks to unfold the activity which calls forth the counter-colour. This is an example showing how the environment can influence a child.
In a similar way the child is influenced by everything which surrounds it, in addition to many, many things which I shall explain later, in another connection. All this contributes to a very great extent to the development of the child’s physical body.
Source: Rudolf Steiner – GA 100 – Theosophy and Rosicrucianism: Lecture V: Metamorphoses of Our Earthly Experiences in the Spiritual World – Kassel, 20th June 1907