Non vet-reward, red soulstones are not rare on Siege. At one point in time, the samurai helm and ember leggings were blessed here on Siege. In an effort to correct that, the devs removed the blessings and placed a turn-in NPC that would give a full soulstone token as a replacement item. With that, they gave us a choice of color. As long as it is in token form, as shown above, it is a legit and useable item.
Edited to add: If you ever loot samurai helm and ember leggings from a player or an IDOC, take those items to the turn-in NPC in Brit and see if you are offered a token. The blessings have been removed, but the NPC will recognize the ones that were originally blessed and offer a soulstone token in exchange.