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.
In digital cameras, raising the ISO means a similar decrease in quality, with an increase in what's called "noise." It's the digital equivalent of grain and results in a sort of "chunky" look to the image.
