'Blue' - money for bribes
Banknotes with a nominal value of 5 rubles first appeared in Russia in 1786 by the decree of Catherine the Great:
'To facilitate the circulation and circulation of money, we command: to establish banknotes in ... five rubles, which are printed for better discrimination on blue paper ...'.
For a better distinction – this is for illiterate segments of the population, who, although they could not read, were not colorblind, and blue-colored papers could always be distinguished from others.
Folk art has dubbed 5 rubles, respectively, according to the color of the bills: blue, blue, blue and other word formations.
But the people did not limit themselves to epithets – there were also sayings.
Bribes to officials are a very original and widespread phenomenon for Russia: even the 1st governor of St. Petersburg, Generalissimo and His Serene Highness Prince Alexander Danilovich Menshikov, in addition to military exploits in the Battle of Poltava, was noted in history by an unprecedented amount of embezzlement.
In other words, the Russians had someone to take an example from, and these examples clothed folk art in capacious metaphors.