The Scottish flag, also known as St. Andrew’s Cross (in English, St Andrew’s Cross), or also as Saltire, is composed of a white cross on a blue background.
The white cross is the symbol of Saint Andrew the Apostle, the patron saint of Scotland. The color of the background of the flag was variable, from light blue to navy blue, apparently depending on the type of dye available in each area and era. When it was incorporated into the UK flag, navy blue was used as the background color. However, in 2003, a Scottish Parliament commission established that the official flag background color is Pantone 300 (i.e. 0, 114, 198 in RGB color model or # 0072C6 in HTML color codes) , a color somewhat lighter than the Pantone 280 of the UK flag.1
The dimensions of the flag are not officially established, although they are usually 4: 5,2 3: 5 or 2: 3. The cross bars should be 1/5 (that is, 20%) of the height of the flag.
According to legend, in 832 King Angus II of the Picts led the Scots in battle against the Angles, commanded by Aethelstan of East Anglia, near present-day Athelstaneford Township in East Lothian. King Angus and his men were surrounded, and prayed for their lives. During the night, Saint Andrew appeared to the king and promised victory. In the morning, both armies saw a white cross appear on the blue sky, representing the cross on which Saint Andrew had been martyred. This appearance gave the Scots courage, while the Angles became demoralized and lost the fight.
The historical evidences of the use of the Cross of San Andrés as a symbol of Scotland are quite later than this legend. In 1385, the Scottish Parliament decreed that Scottish soldiers must wear the saltire as a badge. The first preserved Scottish flag, consisting solely of a white cross, dates from 1503, although the background is red, not blue. By 1540 the legend of King Angus had been modified to its current version, including the vision of a white cross in a blue sky, so from that moment on that was the design of the national flag of Scotland.
From 1606, and especially after the definitive union of England and Scotland by the Act of Union (1707), the flag of Scotland was incorporated into the flag of the United Kingdom, to which later, in 1801, the Cross of St. Patrick, to symbolize the United Kingdom of Great Britain and Ireland.