Fireworks, those that explode in the sky, technically called pyrotechnic stars or aerial shells, have only a few essential components. Once the shell gets up in the air, the main event is fueled by aluminum metal or sometimes a mix of aluminum and magnesium metal. By themselves, these elements don’t burn quickly enough in the atmosphere and the flames they produce are just boring white. So this fuel component is mixed with another chemical that helps the aluminum burn (technically oxidize) faster. Different oxidizing compounds make different-colored flames when they react: purple (KNO₃), blue (CsNO₃), green (BaCl₂), yellow (NaNO₃), or red (SrCO₃). There are lots of other components of modern fireworks (like gunpowder to help disperse these chemicals to make big shapes), but all of the chemistry is based on these simple reactions.