horizon blue might have been a car color - it was not a 1954 Chevrolet truck color
Were you looking at a 1954 Chevrolet car color chart?
Light Blue is in the Bulletin (above) - that would be the Transport Blue
Dark Blue would be the Mariner Blue
Check the 47-55 Truck Colors Tech Tip for original truck paint chip sheets/name/codes.
Note that paint chip colors have been changed by age (as have been the colors on the truck - changed the least, as you point out, in areas not exposed to light/air/wet).
