It is donde with 20 equal equilateral triangles, you need at least 5 colors so you don't get two triangles with the same color together.
Step 1: Making the triangles
One way to construct the triangles is first drawing an equilateral triangle with the same side length as the square and taking the distance from the top vertex to the center of the square with a compass.
Then mark that distance from each vertex of the square to the side on its right (clockwise).
Again with the compass take the length from the other vertex to the mark you just did.
Now you have to make the triangles with the length you have with base on the sides of the square as they are on the picture.
Now you cut all the triangles :D.