That "smoky black" is in fact a smoky black silver dilute (I know the horse, Morgan mare Positively Charmed). "Pure" smoky black most often looks like a faded black, in more extreme cases might be confused with bay - some Morgan examples: http://www.morgancolors.com/smokyblack.htm
The sooty gene creates the appearance of sooty in horses. It is unknown what causes sooty as of now.
I'd remove word "gene" from this bit, as we don't know if it's a gene, a couple of genes or something else
Titbit - sooty horses can change their appearance with age - I've found a horse that was born palomino (DNA tests confirmed palomino indeed) but when he grew up, he got so dark he could be mistaken for a faded black
EDIT: Btw, just to warn you - things might get a bit complicated and confusing when it comes to pinto patterns. W mutations are especially fun
Also, there are some very recent discoveries about dun dilution - I'll write something more later today (hopefully), as I'm going to work soon.