I also agree with Tartan. It's a regular snowball square, within a snowball square. What makes it look so special is the double strip of fabric they used in the outer corners. I can't believe how accurately she got those corners to match!
You would also have to make up a special chart for the color positions of those little corners. It appears that each row of the quilt that the solid corners are (of the four colored corners) are in a different position. Two of the corners are solid and 2 are prints. In one block the solid is on the top next to each other and the two printed colors are on the bottom. In the next row they are reversed. This gives the impression of that the block is harder than it looks.
Snow ball blocks are generally pretty easy. However, this type of layout would drive me bonkers. But, it sure is beautiful when it is put together. Good luck.
Mary Ann