Very interesting lecture on colour today. Colour Workshop notes
Couple of related effects in the image above. Red/Green potentiates ( multiplies the effect) of each other. Secondly red has a higher visual weight than any other colour.
So visual weight is the ability of a region or art element to draw attention to itself. Visual weight is often created through the use of contrast and/or through the use of colour (sic). i.e. the eye is drawn towards the colour ..and the subject.