What green trail was it that was steeper then the black diamond at Canaan?
The trail Boreen at Whiteface, while it has a gentle slope for most of the trail, has several drops along the trail that are definitely not what you would expect from a green level trail. In fact, there is a semi-steep drop at the beginning of the trail and there was one short drop that felt comparable to the Face trail at Canaan Valley. It may not have been as steep, but it certainly was longer than the Face trail at Canaan.
Now, I don't think the Face should be rated a black diamond at Canaan. It isn't any where near as difficult as the other black diamonds at Canaan and it is so short that it really shouldn't be it's own run. I remember skiing Canaan last Christmas when Valley Vista to the Face was the only trail open besides the beginner triangle and feeling lied to by the trail map by how long the Face trail looks on the map when it is this tiny drop near the end of the trail and that it was rated a black diamond.
In reality, Whiteface is not a beginner friendly mountain. They have a couple of true green trails at the bottom of the mountain that have very little vertical. Past those couple of short trails, you really need to be at least an intermediate, and best to be a strong intermediate to ski the rest of the mountain. Liberty and Whitetail have longer beginner trails than Whiteface does.