They close-up of the plug looks a little "oily" to me...ie like some seapage past the valve seals, or rings staring to let oil past... how old are the plugs, year and mileage on the bike?
The rust is pretty common...assuming the plugs have been installed at least a year, and is more common on bike that don't get used a lot...moisture from condensation is the most likely source of the moisture, but it would pay to make sure the drains are clear.