How do fireworks get their fantastic colors?

• The right mix of chemical inside a shell – a cardboard ball or cylinder filled with gun powder charges and “stars” or pellets of chemicals.
• The shell is launched into the sky with a delay fuse lit. Once the fuse burns up, the ball explodes — sending out the stars and setting on fire
• Depending on the chemical composition in the stars, they glow a different color when they burn.
  • Strontium -> red,
  • barium-> green
  • Sodium -> yellow
  • magnesium -> white
  • chlorine and copper -> Blue
  • Color changing fireworks have stars with layers of coating made of different chemicals
• To achieve particular shape like rings or face etc., stars have to arranged in a specific way, or forced to escape the shell in a particular pattern.
• Fireworks experts are called pyrotechnique chemists.
• Fireworks were invented in China as early as the seventh century B.C.

Ref: https://www.livescience.com/37894-how-do-fireworks-work.html