Differences between armors?

I see there are 4 types of armor, Cobalt, Copper, Gold, and Obsidian. They all are in ratings of +1 or +2. Is there any difference between them? Does Obsidian armor have more defense than Cobalt? I don't see any armor rating on the gear, so that is why I am confused. Are they all the same in quality, just a different color?
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