All I can think of is to paint it to look like part of your garden with flowers etc.

I just paint mine as the doors still need to be opened, If you dont open them you could stand pots of plants in front and hang a line of wind chimes along the top

If you're any good with a paintbrush, do a floral painting on it - pale green background, then paint on something you like. If you're not artistic in that way, you can buy cut out shapes made of metal, usually black, like trees, etc., often used down the side of people's houses where it's narrow and dark, or stencil onto the door one or two of the shapes if those are too heavy. Or use a cut out and spray paint. Obviously, you'd need to use exterior oil based paints.

.. or ask the local graffiti gang to decorate it!

If you follow Volunteer's suggestion, though, look for a graffiti artist--not just any old homey--and reserve approval of the design! : )

Proceed with care! You may end up with garage squatters lol

Thanks for all your suggestions. I am a bit arty but the doors aren't flat which makes it a bit more difficult to paint a design. I have to admit though I hadn't thought of trying to do that and may give it some thought. :)

Good luck and have fun...