this would be great

Would it be possible to add this so when you get an epic item in your inventory it shows up with the colored border like what you see in the screenshot, if that makes sense. Would look really aesthetically pleasing for players.

If it was possible I would have done it when the plugin was built.

The item icons are based on their skins. You would need to create multiple skins for each item in order to achieve this, and even then the player can simply reskin the item.