The colour of the stamps is not always random. In the service of international correspondence colors vary according to their use. Initially, the Universal Postal Union adopted the dark blue color for the stamps for postage of simple letters, red for the postcards and green for press rate. Currently these provisions have been abolished and the colors are often used to distinguish copies according to different values. Sometimes, a same value can acquire different shades to the point of being considered an exception, of great philatelic value.

The first stamp in the world, the Black Penny was printed in black, also numerous broadcasts in the early days of Philately. The most usual is that the predominant color either which is indicated in the catalogues of stamps and, when stamps have various colors, refers to the key according to the provision from the edge of the seal to the Center. It is very common to find at the bottom of the various seals strokes, such as we see in the paper money. Importantly, the system employed by the engraver Giuseppe Masini, when in 1858 was the first issuance of Neapolitan stamps. In each of the values recorded at the bottom of the stamp, one of the letters of his name. These stamps were printed in an only color to avoid that the Bourbon flag might formed by combining different values.