Item grades are colour coded in Kritika:
Grey - This colour represents that the item is of Poor grade which is the lowest item grade you can get.
Green - This colour represents that the item is of Normal grade which is of higher quality than Poor (grey) grade items.
Blue - This colour represents that the item is of Rare grade which is of higher quality than Normal (green) grade items.
Purple - This colour represents that the item is of Epic grade which is of higher quality than Rare (blue) grade items.
Gold - This colour represents that the item is of Legendary grade which is of higher quality than Epic (purple) grade items.
Gold w/ a red border - This colour represents that the item is of Hidden (Legendary+) quality which is higher quality than Legendary (Gold) grade but less than Ethereal (Red) Grade.
Red - This colour represents that the item is of Ethereal grade which is the highest grade you can get for an item.