Is this a good science fair idea?

Well i came up with an idea for my science fair where i burn different substances and shine the light of it's flame into a prism, onto a white piece of paper. (this is done on a dark room btw) and take a photos with a god camera (i have one). i then put the photos on the computer and show what colors of the spectra but using the eye dropper to select and show each colour. what substances should i use? is this a good idea? how could i turn this into a scientific question? or does anyone have a better idea?