Trying to describe how I would approach it:
Look at the picture diagonally, as blocks are on point.
Isolate what I will call sashing, although I think it's part of the blocks. Look at only the 9 patch and sashing on two opposite sides as if going across the block. Looking this way, you will see that it looks like a strip with a square that was stitched and flipped to make a triangle on corner. Light blue on the dark rectangles, dark blue one the light rectangles.
While I don't think this was the way it was made, it might work... If, that is, you can figure out what I'm talking about!
There is a tumbling blocks pattern from the series Not Your Grandmother's that makes a TB without Y seams. If you look at that, it might help you. The 3D effect is, in large part, bc of color selection and placement.