Hi (again?)!
I kind of follow the instructions this gal gives and try to grind the nails more like her photos. Our older lab would let me grind away with never a complaint. Our younger girl despises having her nails trimmed, grinded (yeah, probably not a real word), or anything so hers don't get done too often. The way Chase held his feet made grinding them more necessary than Lark, who appears to rest back on her feet more than Chase so her nails don't touch the ground much even if they're a little long. Anyway, grinding Chase's like the instructions doberdawn gives worked well for us, you can angle the grinder such that it gets the nail shorter and it doesn't get to the quick as fast. You may have to do it weekly to get a little bit off at a time to get it all the way back that short. On your pup's nails, you can see the little round circle in the middle is still surrounded by a good amount of hard nail. If you held the grinder more perpendicular to the nail, you could get it a smidge shorter by grinding that top edge without grinding the quick, if you see what I'm talking about.
How to Dremel Dog Nails @ DoberDawn.com
As for the black toenail, has it always been like that or is it something new? If it hasn't always been black, maybe the nailbed got bruised from the length of the nail or something and it grew out dark. If it used to be light like the others, I wonder if it will grow out light again if the length is shortened up some. Otherwise, I guess it's just something that makes him special.