Pan-Slavic colors

The Pan-Slavic colors, red, blue and white, were defined by the Prague Slavic Congress, 1848, based on the flag of Russia, which was introduced in the late 17th century. The tricolor flag of Russia was, itself, inspired by the flag of the Netherlands. Historically, many Slavic nations and states have used the flags and other national symbols with those three colors. Beside Russia, countries that use or have used flags with Pan-Slavic colors include Yugoslavia,Czechoslovakia,Czech Republic,Slovakia,Croatia,Serbia and Slovenia.

Yugoslavia, both the Kingdom (Kingdom of Yugoslavia, 1918–1943) and the Republic (SFR Yugoslavia, 1943–1992) was a union of several Slavic nations, and therefore not only sported the pan-Slavic colors but adopted the pan-Slavic flag as its own (later adding a red star). The later Federal Republic of Yugoslavia (1992–2003); a federation of Serbia and Montenegro, and its successor state, the State Union of Serbia and Montenegro (2003–2006) also used the pan-Slavic flag until the final dissolution of Yugoslavia in 2006. Serbia continue to use the flag with Pan-Slavic colors.

The flag of Slovenia was introduced in 1848, when group of Slovenian intellectuals in Vienna, Austria created the tricolor flag (white-blue-red). Slovakia also has the same tricolor flag design as Slovenia and Russia. The first Slovak flag was also introduced in 1848.

...
Wikipedia