Good use of shadows to really make the petals stand out.

I would've used a different color for the dewdrops, just to make them stand out more, but that's my only nitpick.

 Well as may already know, there's about 7 or 8 colors that are almost exact duplicates of the other ones you used. This can easily arise by a single click or if you changed the hue, saturation, or value by a single point. 

http://img213.imageshack.us/img213/2425/rose1m.png

So I highlighted the colors that are practically the same, and put them on the right side. 

http://img542.imageshack.us/img542/3180/rose2n.png

And here is me changing all of the unneccessary pixels to pure white so you can tell which ones are the sad pixels. 

Anyway, nice rose, but it could have been a little more crisper with clearer geometric shapes. 

Lastly, here is a nifty link, that can check the colors of a piece. (paste the link to this page, and click check then specs)

http://www.hivemind.in/pj/checker/