On my new Nord character my heavy armour is level 23 in green and my Light Armour level 15 in red. Neither skills have leveled and I have no diseases, and I'm not wearing any enchanted gear. What's up withh that?

Check the active effects tab in the magic menu for any buffs. If nothing's there, use player.modav in the console if you're on pc. If you're on console, try turning into a werewolf and back.

No buffs active except my Guardian Stone. Not on PC. New character, not a werewolf.

Get a skill increase in affected skill. It should fix the problem.

^^ this happened to me on a couple of my toon's and leveling up in the effected skill fixes it.