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.
We would buy Rock Candy at the old ZCMI. I always chose the pink ones. I remember the old wood floors and walking up the ramp to the candy counter. The rock candy then was on a string, rather than a wooden stick.