I took all of my spark plugs out today and all of them looked pretty good except for #7. All of them actually looked a little lean, but the #7 was just black as hell! It looked so black it might have even been fouled out. What could cause this?

 

Could be the head gasket, letting oil into the #7 combustion chamber.

Could also be the plug not firing reliably. Try swapping the #7 and #8 leads over (both ends!) as they are the same length. Go for a drive and then see if #8 fouls or if it's still #7. That'll tell you if the lead is breaking down or not.

You can test the resistance of ignition leads, but I have had a couple test ok but still cause misfiring, so I no longer trust this method.

 

Check for a bad intake gasket (across the bottom of the runner), or bad valve guide seal on that cyl.

It's also not impossible that your intake is sending any fuel that pools up on its floor to that particular cyl. Minor details in casting irregularities will sometimes do that. The back cyls are the lowest ones, so fuel is going to want to just run that way of its own accord anyway.