The orange granular powder found in fireworks is potassium dichromate used to slow the decomposition of oxidizers. Calcium chloride produces orange fireworks.
Potassium Dichromate via kwout
In solution, it is used as a surface treatment to suppress the corrosion and reactivity of magnesium; infrequently as an oxidizer; and as a catalyst to aid in the decomposition of potassium perchlorate, often in primes. It does this by lowering the activation energy of the chemical reaction that takes place when the composition burns. That makes the star, comet, etc. ignite at a lower temperature. Potassium dichromate enables the oxidizer to part with its oxygen with a lower input of energy than would otherwise be needed. In other words, it allows the oxidizer to decompose at a lower temperature.
The colors in fireworks are created by the use of metal salts. Metal salts commonly used in firework displays include: strontium carbonate (red fireworks), calcium chloride (orange fireworks), sodium nitrate (yellow fireworks), barium chloride (green fireworks) and copper chloride (blue fireworks). Purple fireworks are typically produced by use of a mixture of strontium (red) and copper (blue) compounds.
Find out more about how fireworks get their colors at Earthsky.org.