Colour balance

Colour balance does present us with a bigger challenge. The colours we see are the visible portion of the spectrum of light; different colours are represented by different wave lengths. Blue has the shortest wave length with the most energy, red is at the other end of the spectrum with the longest wave length and the least energy. Light travels quite effectively through air, so the difference in energy between the colours has negligible effect on how far they will travel and the colour balance will tend to stay the same from the light source until it reaches the subject.

However, the energy is lost very quickly when it tries to penetrate water. We see this as a gradual loss of colours, starting with the reds, yellows, greens and then finally blues. At just 6 metres, a normally vivid red object will appear a rusty and dull brown. Inadvertently stray too close to a coral and cut yourself at 20 metres depth, your blood will run a rather disconcerting green. Down at 40 metres, everything will be swathed in a blue hue.