Blue at (0,0) expanded down to (1,0). Red at (2,2) then overrides (1,0), changing it from value 1 to value 2. So in the masked grid: (0,0) stays blue (value 1), (1,0) is now red (value 2), (2,2) stays red (value 2), everything else is black (value 0). Grid is [[1,0,0],[2,0,0],[0,0,2]].