The following is a list of colours of Legion models that are yet to be reported on a
tameable beast. Have you found any of them? Please let us know!
I've omitted mechanostriders since there are obviously LOADS of colours and they'll presumably be released slowly. I've also omitted single-look mechanicals where nobody has confirmed that the model should be tameable (like the rocket chicken).
Musken
Mana Sabers

- used by
Myonix, but she's not tameable. Was also used as a second colour on the Mana Saber, but it seems to have been removed. Maybe they intend for it to be used on a rare or something?
New Mana Wyrms

-
Maybe? used by the tameable
Bloodscale Wyrm in Suramar, but I haven't been able to find it since Alpha ended.
Moose

-
Possibly tameable? Used by
Well-Fed Ironhorn Bull, which should appear when the Bacon world quest appears in Highmountain, but I haven't seen this quest pop for many weeks and so haven't been able to check its status. Also used by
Majestic Elderhorn (the crazy running moose), but it seems like they don't want to set vignette / quest mobs tameable this xpac. A third white moose,
Winter Elderhorn, is a non-attackable quest NPC.

- only seems to be used by
Morashu (untameable). Morashu is supposed to be some kind of "ancient" power, so shouldn't be tameable anyway.
Does
Stags

- there are a few different tameable white stags in the Isles, but they all seem to use the Pandaren stag model!

: a look from Pandaria that remains unused. I'm including it here because other Pandaren stags have been used in the Isles.
Broken Isles Worgs

- used by two untameable NPCS:
Bloodstalker Alpha (Part of "Worg Pack" vignette) and
Den Mother Ylva (world quest mob and also level 112).
Maned Wolves

- this one IS actually tameable (
Jandvik Ripfang) but that NPC becomes non-attackable early in the Jandvik quest chain, so it probably needs another source.

- actually in the database since WoD, but including it here anyway as it was recently used on
Freyja. Hopefully it'll be used on a rare somewhere.
Boars

- used on one mob,
Leytusk (untameable).
Mechanical Wolves
I'm listing these, but the mechanical wolves are all being treated as special tames, so it's possible they'll want to reserve the last two colours for later.
