Fire Color - Source
Green - Boric acid is probably your best source of "green". Boric acid most commonly is sold as a disinfectant in the pharmacy section of a store. Copper sulfate is another metal salt that produces green fire. You can find copper sulfate, usually diluted in liquid form, in products used to control algae in pools or ponds.
White - Magnesium compounds can lighten a flame color to white. You can add Epsom salts, which are used for a variety of household purposes. I usually see Epsom salts sold in the pharmacy section of stores for use as a bath soak, but the salts commonly contain sodium impurities, which will produce a yellow flame.
Yellow - Your usual fire will be yellow already, but if you are burning a fuel that produces a blue flame, for example, you can turn it from green to yellow by adding sodium salt, such as common table salt.
Orange - Calcium chloride produces orange fire. Calcium chloride is sold as a dessicant and as a road de-icing agent. Just be sure the calcium chloride isn't mixed with sodium chloride or else the yellow from the sodium will overpower the orange from the calcium.
Red - Strontium salts produce red colored fire. The easiest way to get strontium is to break open a red emergency flare, which you can find in the automotive section of stores. Road flares contain their own fuel and oxidizer, so this material burned vigorously and very brightly. Lithium produces a beautiful red flame, too. You can get lithium from certain lithium batteries.
Purple - Purple or violet flames may be produced by adding potassium chloride to the fire. Potassium chloride is sold as lite salt or salt substitute in the spice section of the grocery store.
Blue - You can get blue fire from copper chloride. I am not aware of a widely-available source of copper chloride. You can produce it by dissolving copper wire (easy to locate) in muriatic acid (sold in building supply stores). This would be an outdoors-only type of reaction and not something I really recommend doing unless you have a little chemistry experience... but if you're determined, dissolve a piece of copper in a solution of 3% hydrogen peroxide (sold as a disinfectant) to which you have added sufficient muriatic acid (hydrochloric acid) to make 5% HCl solution.
Do you know of other sources of metal salts that can be used to color fire? If so, please add your comments in response to this post.