Complicated somewhat by wolf being probably the most messed-up model behind the scenes...
There's actually 2 classic-era wolf models: WOM (race 42) and WOE (race 120).
WOM is Wolf Male (the Female variety is the Scaled Wolf model added with Kunark, which is a whole other story...) which is the grey-furred wolf by default, and has alternate textures for black fur and white fur.
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WOE is... probably Wolf Elemental? (Maybe that's what Verant called it? Dunno where early data scrapers got all the race names from...) This is the one with blue fur and red eyes, the "spirit wolf". It has no alternate textures. (Although I feel like it had a semi-transparent mode using the same textures, which would technically work as a "alternate texture" in the client. This seems to be messed up with how p99 made the old wolf models work, though.)
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The fact that the earlier spell data list Illusion: Wolf
Elemental is maybe decent evidence that it used the spirit wolf model, and not the grey/black/white wolf model (could be better evidence if someone knows where the name came from).
On the other hand, the black fur being an alternate texture makes things interesting, because early data scrapers may not have known about one of the spell data fields being used to specify the texture for an illusion. Alternate texture illusions were very rare at the time (red bone skeleton from the necro nuke is the only one I can think of) and, later on at least, they awkwardly put the id of the texture to use into a field that is normally used for spell effects that scale numerically with level.
On the other-other hand, illusions with alternate textures were so rare that it's possible they might have all just been hard-coded at the time, which would escape being captured from the spell data. No reason to assume that, though, and without a post of someone mentioning the color I would err on the side of it in fact being the Wolf Elemental model.