TheWoWDBI don't think it's based on the colors, but rather that it's called the "Redemption Armor". In patch 2.4 when Liadrin realized Kael'thas had betrayed them, she goes to Shattrath and A'dal tells her Velen's prophecy: 'Silvery moon, washed in blood, / Led astray into the night, armed with the sword of broken Light. / Broken, then betrayed by one, standing there bestride the sun. / At darkest hour, redemption comes, in knightly lady sworn to blood.' I believe redemption is what she's after. After all, her horse itself is named 'Redemption': http://www.wowhead.com/npc=77672
Elite
Lady Liadrin
Blood Knight Matriarch
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That's the Blood Elf paladin class mount. Time to roll a Belfadin.
Redemption (her horse) would be a fantastic mount for some transmog sets. I love the burnished colors on the armor and the spikes running along the mane are superb.
Details
This roster comes from the current game client's data files, so it is not a complete list of every NPC in the game - older world NPCs that are no longer in the modern client are absent.
Community notes from Wowhead · 5 comments
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Level and Map Tracking
The game data tunes Lady Liadrin for levels 20 to 40, Warlords of Draenor content.
The map marks it with vignette 3,223.
The map marks it with vignette 3,668.