Final answer:
Copper is the metal that gives some fireworks their blue color, as it forms compounds that emit blue when heated.
Step-by-step explanation:
The metal that gives some fireworks their blue color is copper. Transition metals like copper are often used in fireworks to create vivid colors due to their ability to form compounds that emit specific colors when heated. Copper (II) nitrate, when heated during a fireworks display, can produce a blue flame, contributing to the overall color effect of the firework.