This article uses a good example of a room to display how different colours are used in different proportions can create a variety of effects. It states as a "rule of thumb" to have two thirds of one colours and one third of another which is a nice simple way to look at it and easy to remember.
Things that are perfectly proportioned are more pleasing to our eyes, we search for symmetry for example and balance. In a mess we try to make sense of it and try to find recognisable shapes. Howeverthings that are not proportioned are not necessarilt a bad thing as it can create a more interest and emphasis on a point.



