Since early-XIX century Russian money were: 1 ruble - yellow bill, 3 rubles - green, 5 rubles - blue, 10 rubles - red, 25 rubles - violet, 50 rubles - dark green, 100 rubles - brown and "rainbow".
Unforchunately our new "democratic" power ruined this tradition that was almost 200 years old. It was used to help illiterate people not to get confused with values of the bills.
