Let's see. Polearms, such as your javelins, are a deep blood red. Short blades are dull blue, Long blades are a brighter blue. Axes are almost black, maces and flails are grey. Anything that is or has been cursed ends up being orange.
Poison food is green, mutagenic food is purple, necrotic food is radioactive orange, food that's mostly okay but will sometimes sicken you is soft brown, and regular food is grey.
For general items, orangey red is dangerous (poition of decay), purple is sometimes dangerous (potion of mutation, scroll of immolation), and glowing yellow is very helpful (potions of speed, wands of healing.) If something is displayed in deep grey, it means that it's useless to your character (potions for a mummy, amulet of gourmand for a troll.)
Jesus, why do I know all of this?