Saltire
A saltire is a diagonal cross that runs corner to corner in the shape of an X. The flag of Scotland is a white saltire on a blue field, known as the cross of Saint Andrew. Jamaica's flag has a gold saltire.
The saltire is also part of the Union Jack, which combines the crosses of England, Scotland and Ireland. Because the arms run to the corners, a saltire changes shape with the flag proportion. It is steeper on a 2:3 flag than on a 1:2 flag.
The flag maker has a saltire layout. Recolor the cross and the four triangles of the field separately if you want more than two colors. The flag design ideas guide puts the saltire next to the Nordic cross and other cross layouts.