STEPS TO REPRODUCE 1. paint 50%red 2. paint 60%blue on the red OBSERVED RESULT Abnormal color in overlapping part EXPECTED RESULT The overlapping part is blue
The Greater blending mode mixes when overlapping, so this is expected behaviour.
@thetwo: You'll find a tutorial on a reason to use it here: https://www.youtube.com/watch?v=4S7uzXL8Dl4