In Colour Therapy, Red, Orange, and Yellow are referred to as magnetic/warm colours - Blue, Indigo and Violet are referred to as electric/cool colours.
Generally speaking, the three higher colours are calming, and the three lower colours are stimulating and green is the balance between the two types of energy.
The diagram on the right, shows the seven rainbow colours in order of their frequency.
Violet is at the top of the column since it has the shortest wavelength and the highest frequency.
Red at the base with the longest wavelength and lowest frequency.
All seven colours of the spectrum can be seen by passing light through a prism. The three 'higher' colours of - Violet, Indigo and Blue are in Colour Therapy Terms called the cool / electric colours and generally indicate calm/and coolness.
The three ' lower ' colours of Yellow, Orange and Red are in Colour Therapy Terms called the warm / magnetic colours and generally these are warming and activating colours. The colour Green is the balance between the cool and warm rays.