How do the Aurora Brealis colours form?

Answer 1

Gases get excited by charged solar particles, their electrons rise to higher energy levels, when the electrons drop down to a lower level they emit characteristic colored light.

Oxygen emissions give green or brownish-red colors, depending on the amount of energy absorbed.

Nitrogen emissions give blue or red; blue if the atom regains an electron after it has been ionized, red if returning to ground state from an excited state.