Barb has it right. There are three different blocks.
1. A colored 4-patch surrounded by white.
2. A white 4-patch surrounded by colors
3. The "cross" block with the little white squares in the corners.
The 4-patch centers can be four patches or could be a plain square.
Half of the blocks are of colored centers surrounded by white. One quarter of the blocks are white squares surrounded by color, and the other quarter are the "cross" blocks.