Your right about the Transport Blue (and maybe even the Mariner Blue) not being quite right, Greg. That "Transport Blue" is a little light - maybe more like the earlier Windsor Blue?
It's hard to depict correct colors on PC monitors over the Internet from scans of 50 year old color chips and GM doxcuments. But,
here is another try. Here's a well-worn sheet of paint chips. Nonetheless, if someone has a truck with original 1953 paint, and it is a shade of blue, it should be easy to distinguish Transport Blue from Mariner Blue.
Here's another truck painted 1953-55 Mariner Blue. 
