You'd think picking colors would be fairly easy, especially since I've had the basics picked out in my mind for the last several years... but you'd be surprised at all the subtleties that come into play.
When I think fall, these are the colors that come to my mind, emphasis on the brown, green and orange. Yellow and red are really just thrown in there because most fall leaves and flowers will have some red in them, inevitably.
Now, keep in mind I know these are bright and a little overwhelming, so most of what we choose will be more like muted shades of these colors. In fact, we got tons of fall flowers 75% off at Old Time Pottery today (which I have a feeling saved us a TON of money) that are good examples of this idea. Of course I can go brighter with ribbons, accessories (ties and the sort), and have some fun with those.
I think I want the girls wearing a slightly darker brown than this, and the guys wearing much darker (chocolate brown, almost black) pants with white shirts with either orange or green ties and coordinated flower boutineers. David can wear a dark chocolate brown suit (with jacket) and the opposite color tie. A good chunk of the wedding party lives out of town so I'm thinking of getting some fabric swatches I can mail out and have the girls pick their own dresses (I reserve the right to veto, of course, but I trust my girls. ;))