First, we would need 6 new game items: CRYSTAL FRAGMENTS. There would be red, orange, yellow, green, blue and purple crystal fragments. These would drop from the auto boss spawns at a rate of 1/100. (either different monsters drop different colors, or random...both could work) these could be mined too, of course, but i think they should be VERY rare.
Second, you go to the witch by the blacksmith to combine the crystal fragments into an ENCHANTMENT CRYSTAL. Six crystal fragments of the same color would create an enchantment crystal of the same color (six red crystal fragments = red enchantment crystal etc...) ALSO, one of each color crystal fragment creates a rainbow enchantment crystal. This gives us seven types (or colors) of enchantment crystals.
Third, the witch can combine an enchantment crystal with any gear item to create the enchanted item (red enchantment crystal + swamp bow = red swamp bow) I think the success rate should be 100% since crystals are rare, you need several of them, and we don't want to discourage/anger/sadden everybody.
The artwork of the item could stay the same, just change the background to reflect appropriate colored enchantment. (Trying to keep it somewhat simple ; )
The value of the item would increase by a lot (maybe 10 million... Minor detail...figure that out later)
The item stats do not change. (bear with me, you'll see)
When a player has equipped four (4) (or more, of course) of the same color enchanted items, he/she gains the bonus (for example: red Odin helm, red swamp bow, red boots, and red mithril plate --OR-- rainbow sword, rainbow shield, rainbow helm and rainbow armor etc...) The bonus is as follows:
RED: STR x 1.2 + 100
ORANGE : ARM x 1.2 + 100
YELLOW: DEX x 1.2 + 100
GREEN: +1 walking speed
BLUE: +20% mana Regen rate
PURPLE : + 20%health Regen rate
RAINBOW: + 20% Experience gain in pvm
It'd create trade of crystals and fragments and enchanted items, give value to items after you "outgrow" them because you may not want to step up to new level gear and break your enchantment bonus etc. It would, in a way, create seven types of each class... Diversity is good

I'm sure somebody can improve the idea some... Fire away
