 The stamps are primarily engraved, almost all in a single color on plain white paper (the $1 seaplane is in two colors).Some of the denominations also received special service inscriptions in black, such as "Bulk Rate" or "ZIP + 4 Presort".Many of those denominations were unusual decimal rates, such as 16.7 or 24.1 cents, used by bulk mailers and other businesses who also used precancels.