Answer:
Due to difference in the electronic energy level of atoms in different metals.
Step-by-step explanation:
The subatomic particles are protons, electrons and neutrons.
When we talk about colors, the subatomic particle involved is electron.
An atom of a metal absorbs light and in this process the electrons gets exited (gain energy) and when they come back to ground state they emit light and thus the color appears.
In case of different metals the energy required for excitation of electrons is different (due to difference in the arrangement of electrons in the orbitals and difference in effective nuclear charge), thus the electrons in different metal atoms absorb light of different of wavelengths and end up in appearance of different colors.