The Saltire is the national flag of Scotland. It is also known as Saint Andrew’s Cross. It has a very long history. Until 2003 it was defined as a white cross on a blue background and many different shades of blue could be found. It was then decided that the ‘official’ colour should be Pantone 300, although this is only a recommendation and the flag is still often seen in much darker shades.

In normal lighting the cross never quite disappears when you look straight at this illusion. The cross is such a well-defined shape that you can often see a slight shadow of it.