Red Ring is a rare barrier that is considered to be the best barrier in the game. It is equippable by all classes, provides passive HP and TP regeneration and gives a +20 boost to all stats along with a decent set of resists.
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Black Paint can be used on a Red Ring to cause it to cosmetically change into a Black Ring. (keeping the stats of the original Red Ring)
However, as noted, the passive HP and TP regeneration do not work with the painted variants.