New York's Empire State Building changes its colours several times a year.
It turned orange, white and green for St Patrick's Day, red and green for Christmas - and even went dark to commemorate the Brussels terror attacks in March.
But now the 102-floor skyscraper is going blue to mark United Nations Day.
October 24th marks the anniversary of the entry into force in 1945 of the UN Charter - known as UN Day.
The Empire State Building is lit up in UN blue | Image via @unngls on Twitter
The founding document was ratified by the majority of its signatories, including the five permanent members of the UN Security Council.
This officially put the United Nations into being. It has been celebrated as United Nations Day since 1948.
In 1971, the United Nations General Assembly recommended that the day be observed by member states as a public holiday.
The human rights body says this year's day will be used to highlight concrete actions people can take to help achieve the Sustainable Development Goals.
