Why are gas giants colored the way they are? As I understand it, Jupiter, Saturn, Uranus, and Neptune are all made primarily from varying proportions of hydrogen and helium.  Despite this, Jupiter is very red, Saturn is yellow, and Uranus and Neptune are blue.  Why the difference in colors for planets with similar chemical makeups?  Or do they not have similar chemical makeups?

If such an explanation is available, I would like specific descriptions of why each planet is colored the way it is.
The simple answer is that the composition in terms of elements doesn't matter for the colour, since that is determined by the molecular composition as well as state (pressure and temperature) of the visual layers (which contain a small but significant fraction of other elements than H and He). Given the differences in the giant planets temperature and pressure, this molecular composition is most likely different.