They mention that 0 is the perfect score, though I'm not sure how the highest and lowest they mention relate to one another (let alone how someones score could be that far off), but I also got a score of 2 and also in Night Shift mode. My weakest area was 17 (a greenish-teal like slice of the spectrum), which would make some sense in how yellow/orange relate to the colors green and blue.
Hum... I thought 0 was the lowest score :)
(Made 2 by the way, but maybe the night shift on my phone have something to do with it)