Although the Packers wore blue uniforms throughout most of Curly Lambeau's tenure, much of the (admittedly rare) merchandise produced during that time was emblazoned with the green and gold which has since come to define the team.
Consider this pennant from the 1944 season:
Blue and gold uniforms, but a green and gold commemorative pennant. It's true that there wasn't as much of a direct focus on team colors as there is today, but even so.
The Packers would continue to list "blue" as an official team color well into the 1960s, perhaps because they were still wearing the old blue sideline capes.