After ten years of existence, the range of "blue" banknotes is getting older and no longer offers the necessary security guarantees. At the beginning of the year 1871, the Bank of France then appealed to a great chemist, Marcelin Berthelot. The latter must think about the possibility of printing the future banknotes in two colors. After many tests, it is a ocher color that is adopted to accompany the blue print. In 1874, the 20 francs Type 1873 Bleu et bistre (Pick: # 61) became both the first two-color bill and the symbol of the switch between the monochrome emissions of the nineteenth century and multicolored banknotes of the twentieth century. However, its broadcast is quickly suspended and will resume only at the beginning of the First World War. Despite this important technical innovation, the Banque de France continues to issue four new monochrome denominations with a 100 francs Type 1882 À filigrane dégagé (Pick: # 63), a 50 francs Type 1884 Indices noirs (Pick: # 62), a 500 francs Modified Black marks Type 1863 and a 1000 francs Modified Black marks Type 1862. This series of notes is quickly replaced by similar banknotes but printed in two colors. The ocher color is replaced by a pink that is more resistant to photographic counterfeiting. The 500 francs Blue and Pink Type 1888 (Pick: # 66 and # 88) is the second banknote printed in two colors and urgent, to replace the 500 francs Black marks Type 1863, victim of a large counterfeit. In less than a year, between 1889 and 1890, the last three banknotes of the "blue period" are renewed and passed in two colors: the 100 francs Type 1888 Bleu et rose (Pick: # 65), the 50 francs Type 1889 Bleu et rose (Pick: # 64) and the 1000 francs Type 1889 Bleu et rose (Pick: # 67). A two-color note of 100 francs Type 1892 Bleu et rose "not issued" (Pick: #NA), drawn by Daniel Dupuis and Georges Duval, is printed and kept in reserve. It will eventually be overprinted and used in several overseas territories. In 1891 began a reflection on the possibility of printing in several colors. Following a long implementation, the 1000 francs Type 1897 Flameng "not issued" (Pick: #NA) is launched in manufacturing, but the Bank of France finally gives up its issue.