More stark means very plain or clear, without anything extra.
Starker can make people think of something very simple or very clear.
Examples:
The room was starker than I expected.
The starker the picture, the better.
The starker the better, I always say.
I like my pancakes starker than yours.
The difference between the two is starker than you think.
The starker the better, that's what I always say.