If memory serves correctly, serial numbers starting with E (printed by CBN) were light blue in color, while prefixes starting with A and B had a darker blue color.
Also, in the two-letter prefix era, the FA-FZ and IA-IZ series were printed in light blue ink, if I recall.
Each of the printing companies used different blue ink, if I recall. Also, if you look closely, the look of the $1 bills printed by CBN and BABN appear to be different shades of green, which proves tbat each printer uses different inks.
The light blue serial numbers started circulating by 1984, as I remember seeing a friend who had a $1 EAB prefix in February 1984. They eased up when the AL* prefixes resumed production, but the remainder of EA* up to around ECF or ECG were likely released before the AM* prefixes around 1986 or early 1987 started appearing. The final year of printing $1 notes took place around 1988 or early 1989, and started around ECH but ended at ECW, though ECV and ECW was not broadly seen, if at all.
The light blue serial numbers were quite abundant across the board during the $1 note's final months in circulation, it seems.
