The dark blue for 1957 trucks was marine blue. I think the same as previous mariner blue. Who knows what was actually used on that auction truck. Royal blue or baltic blue are not factory correct anyway. Check the link for the factory color chips and two tone options for that year of truck.

http://www.tcpglobal.com/autocolorlibrary/

Ed Fallon
In seemlingily endless process of restoring a stock 1953 chev 3100 pickup.