Blizzard has released a new blogpost highlighting the Ensemble: Burden of Unrelenting Justice transmog set, awarded alongside the Trading Post Enthusiast achievement for completing the monthly Trading Post journey twelve times beginning in January. The months do not need to be consecutive however, so players who missed a month will still obtain the achievement and set upon reaching 12 total months.
Originally datamined in Patch 10.0.5, this Warden Transmog matches the Ash'adar, Harbinger of Dawn mount, which was also available as a monthly trading post reward, although it has received some mixed criticism from enthusiasts due to its color shifting nature.
While certainly unique, there does not appear to be a static version allowing players to choose one coloration or the other, making it difficult to match with other partial transmogs, and while the skin color of the spectral tiger does change between white and gold, its own armor remains green and gold at all times, which doesn't match particularly well with the night time white version of the set.
The Ensemble: Burden of Unrelenting Justice pairs with the Ash'adar, Harbinger of Dawn mount, though not all the colors change to match.