Hummmm.... Interesting, so weapons no longer have durability. Well this is just my theory but: What if it has been replaced with the weapon condition?
According to some pics, there is a box behind the weapon icon with different color, maybe it represent the status of the weapons: Bad, Good, Best... Somethings like that. And the condition would affect the Might or Critical? http://serenesforest.net/wp-content/uploads/2015/01/nohr4.jpg
If you look closely at the bottom of the weapon, there is a Color Bar too. When the bar went down to empty, it would change the weapon condition to worse than the normal weapon. That's why it has so many color. Also one thing I noticed that, the enemy is clearly pair-up in this pic (Sorry if i had any mistake in grammar, English is not my native language :) )