As far as color goes, I'm more of a tan/khaki fan rather than light grey. As far as material, I think it depends on what the event is. Personally, I like my cotton slacks. I might even go for a lighter wool blend or a wool/silk blend.
Cotton. It's going to be a little less expensive and it won't wrinkle all to be damned when you sit down for a while when you're wearing it. Linen crushes to easily- you end up a wrinkled mess when you wear it for more than 5 minutes.