These very small red boxes, started in the mid to late 40s. However the Carb. boxes and some of the big cabs were red starting in about 1938. Here is the General rule, Emerald Green is early to mid 20s, Black late 20s to early 30s. Gray early 30s to mid 40s. Dark Gray green early 40s. This is the gereral rule and there are some exceptions.