Why does each compound produce its own unique colour?

Each compound produces a different colour because they each release different amounts of energy. The amount of enegy release willl determine the colour or the wave length of the amount of light. This ocurs when high energy electrons jump to lower energy levels, this creates wave lengths which creates the colour.

LiNO3 –> Red

Cu(NO3)2 –> Green

KNO3 –> Light Pink

Sr(NO3)2 –> Red/Orange

Zn(NO3)2 –> Orange/Yellow

Ca(NO3)2 –> Orange/Yellow