I'd probably go for a white Cuprinol sort of paint, as you can easily re-coat it when the inevitable grass stains appear, or the mud splatters everywhere, like it certainly does here...
It's actually not a bad idea to make it all a bit brighter, but depends on how you're using your shed, a safe haven, a junk room, a carpentry bench-room, a place to pot on things etc...
Like Mum's shed above, we have 'S' hooks nailed all around the walls and shelves, and hang everything up...