Hi Faye --
The color of a flame depends on the material being burned. There are lots of fuels that will produce blue flames when burned; the most commonly available one in the household is natural gas. You can look at the flame on the stovetop (if your stove uses natural gas) or furnace to see a pretty blue flame (don't get too close! These are hot!). Natural gas, or any other pure hydrocarbon such as butane or propane will burn a light blue.
Some flames are yellow because of the presence of a small amount of sodium atoms in the fuel. Sodium atoms glow yellow very brightly when they are heated; yellow light is their very favorite color to emit (this particular shade of yellow is called the "sodium D line" because of the electron orbits involved in the sodium atoms before and after the light is emitted). Sodium street lights are very very yellow for this reason.
Other flames are yellow because of bits of soot, which don't get hot enough glow bluish. Most of the sources we've seen say that this is the main reason for wood fires being yellowish, not the presence of sodium.
Other chemicals make flames burn other colors. Here is a nifty web site listing what is added to commercial fireworks to make them glow all the different colors: http://chemistry.about.com/library/weekly/aa062701a.htm
This site lists copper compounds as good sources of blue (in case the site goes away someday, here is the "blue list"):
copper compounds + chlorine producer
copper acetoarsenite (Paris Green),
Cu3As2O3Cu(C2H3O2)2 = blue
copper (I) chloride, CuCl = turquoise blue
The color of a fire won't depend on what you use to start it, however, just what is burning at the time.
Tom (mods by mbw)
(republished on 07/24/06)