Place 2" Color 3 squares right sides together to
opposing corners of Color 2 3-1/2" squares, with outside
edges aligned. ( I show them staggered here just so you can see what
pieces I mean- yours shouldn't be) On the back of the small squares
draw in the diagonals, and sew on the drawn lines. Cut off the
excess seam allowance, pressing the remainder towards the resulting
corner triangles. Make four units like this. Trim them to measure
3-1/2" if needed...