[Keeper of Dol Guldur]

I can't believe anything in the History of Middle Earth is 'lawful canon' as far as the story goes.

I believe if something doesn't make it into the actual story, all versions aside, it isn't canon.

However, the thing about Balrogs and the HoME are that, aside from not being canon, it does give some more evidence at least to what Tolkien originally envisioned things looking like. Of course, if those depictions didn't make it to the books, tough break.

Anyway, it's not that hard to depict / draw / render something with vague features. Just use lots of black.

The darker, the more accurate. After all, if the Balrog's shadow was enough that it actually smothered out and blocked view of a gaping rift filled with fire, it must have been pretty dark.

Anyway, if you look at things this way, you'll get another notion.

The Lord of the Rings (let's can all Silm references for a moment) was supposed to have been written by Frodo and Sam, with a lot of account filled in by Merry and Pippin, and a fair bit of old history and higher matters that happened told to them by Aragorn. Gimli and Legolas theoretically kept in touch with the Hobbits and helped too.

So the idea is, Frodo (with help) was describing what he saw in that chamber. And it's pretty obvious he didn't see much, if his description is that vague. It seems pretty clear that all the members of the Fellowship could see Gandalf pretty clearly, and the chamber behind and around the Balrog was pitch black, filled with smoke.

The only thing that gave the impression of man shape in the darkest of dark places was probably the fact that the Balrog's hair (hair-like shape) was on fire, and highlighting the "humanoid silhouette" of the Balrog from behind.

Trying to humanize, or even 'demonize' the Balrog in the traditional 'demon' sense, just doesn't do it justice.

It's a spirit of fire, which is physically incarnate and wrapped in shadow. Fire, shadow ... neither thing has solid substance (clearly the Balrog does, otherwise Gandalf couldn't have grappled with it or stabbed at it). If it had no solid mass, it's own weight falling off the mountain couldn't kill it, and it wouldn't have needed wings to fly, being a gaseous entity.

Well, that's my two cents for the moment.