My guess is to simulate how the colors will look on paper, they always look like they "pop" (god I hate that word lol) on a screen more than when printed out. You can turn it off by clicking "noise" at the top right.
The Swiss style seems to have influenced the covers of a lot of old sci-fi books, so I mentally associate these kinds of color schemes with faded old paper and sitting indoors on a rainy afternoon.
