17 out of 20. Was super easy until #10 and I had to stop and think more carefully (which was actually my first mistake), and then I got #14 and #15 wrong. The score was about what I expected, though - would've been surprised if it was <15 correct.
I wonder how much of this would come down to screen calibration / color accuracy? If everything's consistently off in 1 direction I guess not much, but I would imagine certain shades might appear effectively the same on some cheaper screens?