[Phantasm]

I'm going to assume you mean the Greek Gaia, the primordial earth goddess worshipped by the ancient and Classical Greeks as the embodiment of the very earth they stood on, mother to the sky (Ouranos, via parthenogenesis), Titans, Giants, and monsters alike.

In this case, I'd have a small bowl of earth, a mirror to reflect the sky, and a few seeds to represent wild growth. A mat for laying it out on an altar (makeshift or regular) would probably be brown or green, possibly incorporating both.