my thoughts so far - paint some colorful stripe pattern on the walls - say olive green/yellow, put some low-maint planting on both sides of walkway which already have soil in them...maybe stain concrete? maybe paint the front metal gate white so it looks less like a jail? I am not a designer though...thank you.

Paint the fence and gate white to avoid that jail look, as you say. If tenants are responsible for upkeep, then I suggest low maintenance plants such as ground covers installed to cover the ground as thoroughly as sod. The kids bikes will inevitably go on the dirt or planting area. If you have a gardener to do upkeep, then a tough sod would be an excellent choice.

What about a pale blue? Different from the usual B&W choices.

Hi, thank you!! One quick point - I dont want to treat this as just an income generating property, want to get a "wow" factor going here. I am hopeful that with planting + paint + inspiration, I am hopeful I can...here's one I did with a designers help at another of my rentals http://www.flickr.com/photos/prgupta/8562582508/

I love that idea, lime green and red. What do you think of attached, painting something like that on the main walls. Too much?

If those bars are iron, try a terra cotta or coral paint. Then rust won't show so rapidly as it will on white. If you are in a southern zone, use bromeliads for WoW without care. Evergreens would probably do the trick in the North.

How about some ornamental metal work on the wall. Add a flowering vine to climb a trellis and the fence. Hard to see what is in the courtyard to design with existing trees on shrubs.