Mark- Interesting questions. Actually, there can be lots of energy or
very litle energy in any color of light. One of the peculiarities of
quantum mechanics, though, is that the energy comes in lumps of
different sizes, depending on the frequency. When a molecule absorbs
light, the amount of energy absorbed in one step is twice as big for
twice as high a frequency.
I don't know how much different types of fish are affected by light of different colors.
Certainly if the atmosphere let different frequencies of light
through, the world would be very different. Plants, for example, are
specialized to use the frequencies that reach them to make chemical
energy (via photosynthesis).
In fact, human activity has changed the frequencies of light that
reach us because pollutants reduce the ozone level in the upper
atmosphere, allowing more ultraviolet light through than before. That
certainly causes more skin cancers, and may have other very serious bad
effects for various types of life. Fortunately, international treaties
have reduced the amount of the worst ozone-destroying pollutants, so
this problem may gradually get less severe.
(published on 10/22/2007)