The number and pattern of the lights on the cab top give a visual code to the size and height if the truck.
Before the ICC made the standard for all interstate trucks, individual states had their own regulations.
Some of these used colored lights. Amber, red and green were used.
Some of the states kept their instate regs for a while after the fed standard came out.
That is one of the reasons that the factory didn't install the lights until some time in the fifties. Dealer installed before that.
