In the mid-1950's, AASHTO relaxed its restrictions on the designs of
US highway signs and a few state, including Arizona, began to experiment with colors to aid
motorists. Route signs were colored by direction. This scan of the 1956 Official Highway Map
shows the color scheme; however, a color photo from the era shows the the color are really
white letters on a green background, white letters on a blue background and black letters on
an orange background. We are unsure about the brown. Furthermore, Arizona dropped the "US" and
the line from its signs and the signs were silkcreened rather than embossed.
By the late 1950's, Arizona adoped the current style US highway shield but continued
using colors in the background area (the black area on current signs). The color program was
also extended to state route markers. According to Official Highway Maps from the era,
the colored shields were gone by 1965.