Skirmish Hall - Why Can't you Select Unit Colors?

[:1]All the screen shots and videos for the skirmish hall don't show an option for selecting your unit colors for your faction. Why is this? Additionally, I never understood why MS used colors such as yellow, pink or purple for units (why not try more realistic color palletes - tan/khaki, olive green, gray etc.)? We would still be able to see the units easy - total zen killer for me seeing the Persians in purple!!!!!!!