Flame Color Info in Gas Water Heaters/Furnances

Can somebody explain the different flame colors seen in a gas water heater and gas furnance and exactly what the different colors mean. What color it should be, what color is ok, what color is bad.

thanks.

http://www.inspectapedia.com/plumbing/gasfaults5.htm

http://www.gascape.org/HomeGasTest.html

http://www.appliance411.com/faq/gas_range_flames.shtml