Rarity

Rarity is a statistic applied to items and blocks to signify their value and ease in obtaining. The only effect rarity has on an item is the color with which their name appears when selected in the hotbar or moused over in the inventory, and has no effect on gameplay whatsoever.

The only way to change an item's rarity is to enchant it, which brings its rarity to Rare from Common or Uncommon.