Taking one each of the contrasting main triangles place them with the right sides together.
Sew around the triangle with a 0.5cm seam allowance leaving a gap along one edge to be able to turn the shape through.
Clip the corners and turn the right way.
Place the triangle with the brighter of the two fabrics down and find the centre of the triangle.
Fold down each point in turn, to the centre and secure with a few stitches. This will create a hexagon shape.
Push the needle through the centre of the hexagon and flip it over. This will give you the centre on the other side. 
Bring the middle of each of the flat sides into the centre and stitch down through all the layers.
Flatten the corners and press to ensure all edges are the same length and the points are sharp.
Do this for the other 9 triangles.