What relevance are the colours during meditation
Colours vibrate - red, being the outside of the rainbow, vibrates with a much greater wavelength than orange and then orange is greater than yellow, and so on. So when you go through the colours of the rainbow, starting from red and finishing with violet, then this is used as an induction process to take you from the Alpha brainwave state to the Theta state. The Theta state is the meditation state. As we go through the colours the vibration is getting finer and finer - this is what takes us deeper.