The chord wheel shown here is actually two separate pieces when printed.
There is the main blue portion printed on a standard paper, and then the sun portion with its thick outlined boxes, which is printed on transparency paper.
This allows the sun to be rotated along the wheel to show which chords work harmoniously in music.
It's really good for people who want to make music and understand chords, but aren't the best judge of what chords will work well together. It's also useful for general "jamming," and simply joining in and playing along with other musicians.