If you do not want to use actual flames in your science project, consider creating a Bristol board presentation that explains why burning different chemicals produces different colors of flames. Explain that the electrons active within the atoms of the flames can only have certain specified energy levels. As the electrons jump up and down their available levels of energy, we perceive the differences as changes in heat output and the color of the visible light. Use pictures of different colored flames and identify them as having higher or lower levels of energy.
For more advanced students of chemistry, you might want to try actually burning some of the chemicals that are responsible for the changes in flame color. Be sure only to do this under the direct supervision of a qualified teacher. Using a very low flame or smoldering embers, carefully add different kinds of chemicals and record the effects. Use 125 grams of cupric chloride to produce a blue flame. Add 1 lb. of borax to produce a green flame. Pour in 100 grams of potassium chloride to produce a purple flame. Make sure all measurements are accurate.
Like burning different kinds of chemicals, colored flames can also be produced by burning metal salts. Burning metal salts brings the electrons in the metal atom to a higher energy level. The flame change color as it gives off energy in the form of light so that it cannot return to its normal state. Certain metal salts create sparks of different colors in addition to flames. Try burning a 12-inch strip of magnesium ribbon to create white sparks. Burn 1 lb. of iron fillings to create yellow sparks.
If you are advanced student of chemistry, i.e. university or graduate level, consider experimenting with different combinations of chemicals. This makes an interesting graduate-level thesis, for instance. However, it can be highly dangerous. Never attempt to mix two chemicals whose reactionary properties you are unfamiliar with. Ask your supervisor for advice and guidance on how to do this safely.