Purple Patch

The Purple Patch is in reference to a small update to the game where the developers increased the difficulty of enemies that were four or more levels higher than you for minions. Higher level enemies got a boost to both their defense and offense making them much more dangerous to fight. Purple refers to the Con System in the game where enemies four or more con levels will have their name appear as purple in the target window.

Before it was implemented, full groups of heroes were able to defeat enemies that were ten levels higher. This was against the game design so the "purple patch" was made.