Colours

Gold - depiction of 'daylight'/sun, goodness and general positivity

Silver - depiction of 'night'/moon and, potentially, negativity

Green - Life, including the Prime more generally

Purple - still seems to represent evil influence but references are mainly historic so far
[Edit by Dunsi - in the present it clearly means "noble and brave loyal Gnome hero"]

Metals trapped in stone often have different colours to represent different races