Then sew Color 2 quarter square triangles to opposing sides of
the Color 1 2" square. Press seams to outside. Add two more
QSTs to the remaining two sides of the square, again pressing to the
outside. Now sew Color 3 half square triangles to opposing sides,
pressing outward again, and lastly add the remaining Color 3 HSTs
and press to the outside. This is the block's center unit, and it
too should measure 3-1/2" when complete...