In literature or poetry, colors are used as symbols to represent ideas or feelings. The color green is generally associated with money and jealousy. Also, it is considered a color related to rebirth because in spring plants growth and go back to life and it symbolizes new or better things. According to this, the color green is not used to symbolize purity as this is associated with the color white.
I think the answer is 'purity' as it makes the most sense. Purity is represented by the color white, while green is either jealousy or happy/calming(rebirth). New ideas can be symbolized by green, as in a green flag or a green light.
