Well what I do is use the federal standard codes (when I find them) and if I am not satisfied with the result, as in some cases they come a bit brighter than they are supposed to, I just slap a levels adjustment layer over them and fool around with that slightly. In the tomcat I went for a darker result by choice and I also used a vibrance adjustment since I was getting very vivid results but still the colors register as they should I believe...
This way I believe you are closer to the actual color.
Color picking from a photo can drive me mad. I can pick at least 5 different bluish-gray from the image you shared!
Anyways, not saying that color picking is wrong and I really like your result. In some cases you can get good results, it is just a bit of gambling as I see it.