In terms of what you'd see, an atom in the ground state wouldn't emit any light because all the orbital electrons are in their lowest possible energies in the atom.
A ground state atom has its orbiting electrons all in their lowest energy states consistent with, I think, the Pauli (nobel prize winner) exclusion principle and Hund's rules.An excited state atom has one or more electrons in higher energy states - say by thermal agitation (heating them). When these electrons "de excite" back to a lower energy level, they emit electromagnetic radiation in the form of photons. With the correct energy/frequency the photons are visible as a spectrum.