The green colour seen in firework displays is due to the chloride salt of :

The red, orange, yellow, green, blue and purple colors exploding in the night sky during a pyrotechnic festival are created by the use of metal salts. Barium chloride provides green colour to firework displays. Metal salts that are commonly used in firework displays include: strontium carbonate (red), calcium chloride (orange), sodium nitrate (yellow), barium chloride (green fireworks) and copper chloride (blue fireworks).