Combustion, or burning is an exothermic chemical reaction, resulting in the production of light or heat or both. The reactants include a fuel and oxidant. In this case, the problem that you are exploring is if color affects the rate of combustion? This problem could serve as a title that immediately points out what direction your experiment is going to take. Will a white or a colored candle burn at a different rate? Obviously, the composition of each candle may vary in terms of whatever additive is in the colored candle; this additive will not be present in the white candle. This would be a variable that could result in a different rate of combustion. Good luck with you experiment/project!