you have to plan a little bit to stitch your 1/2 square triangles, but if you cut 2-4" squares; place them right sides together, draw a diagnal line across the lightest one, stitch 1/4" on each side of the line, press flat to set the seams, cut on the line, press open;
when you trim you should have 2- 3 1/2" (1/2) square triangles...perfect & easy :)