Hey! Welcome to the forums.
That's a nice start to your umbrella, especially the fold-up. I'm not really a spriting expert whatsoever, so I'd love to have someone experienced in that field to put in their say, but I'll write this in the meantime. Take it as you will!
Although it depends on the light source, it'll probably help to look how the folds of an umbrella top-down would look like. I stumbled upon a few images through a quick search.
I suppose you should pay attention to how the folds work, and that's there a bright side and a dark side to everything. That's the basics of shading, really. Whatever the light source is directly hitting should have the brighter values, and whatever's getting the short end of the stick's getting the darker values. It's kind of hard to tell how you'll work your light source in exactly with that top-down, but I'm assuming the light source is somewhere at the top-right, so try matching that?
You can also read up some spriting tutorials on shading and textures. Here's one I read before. I hope it helps.
http://opengameart.org/content/chapter-4-shadow-and-lighthttp://opengameart.org/content/chapter-7-textures-and-dithering