It shows different shades of green. Therefore I can use it to find the right shade of green for the bits in the light and the bits in the shade; and also to work out which colours I can use for Spring, Summer and Autumn.
I would love to see a tent filled with a "forest" of helium balloons attached to funky strings such as these. Kids would love it! (Blowing Up: 25 Easy, Inexpensive, and Totally Unexpected Ways to Use A Balloon)