I would suggest one focal point wall painted John Deere green with huge logo painted on the wall other walls neutral. Maybe sleek black furniture , black rolling toolboxes for night stands, etc. when he gets tired of John Deere then just paint over the accent wall and you're ready for the next theme.

Think of it as a cheerleader skirt look. Start with the ends and keep splitting center and adding the pleat. until you have the fullness you like. The back technically has the folded pleat and the front is the side with the folds. Hope that helps.

How about flanking the window will billy bookcases? Paint over the green wall an off white and just pick a color you love for the bed wall. A stylish chair for your desk and maybe "industrial" looking bedside lamps will "man" it up. :) Plus, get a cooler looking desk chair...in a color that you paint the bed wall.

OK - I'm a beginner here on Houzz so my opinion isn't worth a lot but here it is: the room is a bit bland and lacking in character. I think you have to find some pieces you really love to bring it alive. All the suggestions are good for widening your horizons, but ultimately, you need to find things that matter to you, because it's your home and not a magazine photoshoot. That said, if it were me, I'd throw a couple of small, colorful rugs down, and put either one large painting or three smaller ones over the bed - not in a line but at different heights - to break up the binary look. I'd also put something on the wall above the heater. Then, play around with a few cushions and maybe a quilt that picks up some of the colours in your artwork.