I have not had much luck with "almost a match" paint color services. The only exception would be one of those small local paint stores that carries a higher end paint and has helpful staff. They seem to enjoy the challenge of trying to match a color perfectly.
I recently had the joy of picking colors for my addition. It was such a headache. The little sample bottles of paint ended up being my best friend. Hubby and I thought we had really accomplished something once we got the room painted. We forgot about what a pain in the butt trim is to paint!
We have been working on our remodel/addition for the past 4 months or so. Of course, since we are trying to do as much ourselves as possible we are terribly behind.
Here is the before and almost after pic of the exterior. EDIT - well, maybe not. Anyway, here is the before pic.