During your battles monsters will drop one or more of 7 types of colored crystals: Red, Blue, Green, Yellow, Purple, Black and White.

These crystals are used to acquire High Tier Equipment. By trading in a certain number of different colored crystals you can get weapons and armor of amazing quality only out done by the Ultimate Sets.

Where do you trade them? You'll have to play the game to find out. Can't spoil everything in the game tips (Hint hint: They are spread out throughout the world, one trader for each color crystal).

So why seven colors? Each crystal corresponds to certain types of equipment effects

Red: Health, Attack, Fire
Blue: Water and Ice, Mana, Agility
Green: Wind, Nature, Defense
Yellow: Earth, Lightning, Luck
Purple: Arcana, Psychic, Magic Attack
White: Light, Resistances
Black: Dark, Negative Effects