Vertical rainbow tetris with middle numbers
This started with a simple verticalization of the previous design but it quickly evolved in very interesting ways. A crucial change was moving the numbers to the middle, which arose when I realized eyes aren't half as good (or half as trained) moving vertically as they are moving horizontally.
The relocation made for a much more balanced design, and that, together with the rainbow color scheme, and the natural gracefulness of squares made this one of the most aesthetically pleasing designs.
Also, I used Luis Pabon's idea of colored lines to mark a month's ending--a marked improvement from little red triangles.
In minimalist overreach, I took away the months. They felt so extraneous to the clear-cut design that was emerging that perhaps the 12 colors I was using (and the fact that months were evenly split up and down) would prove enough to obviate them.
User testing proved they weren't, at all, and the next design evolved in an effort to try to fit them back into the design.