In relation to my new GP9 loco in CN green/gold/black livery I was recommended to check-out this oil-paint dry-brushing technique to sun-fade the paint: http://tws-rustbucket.com/index.cgi?board=bucket&action=display&thread=90  at the RustBucket.com site....sorry but you have to register for this site if you want to see it.

I decided to give it a try on some boxcars so I bought some brushes and a tube of paint and went at it.  The pics on the left of the page are before and the ones on the right are after.