(least sum of) squares

This is an attempt to minimize the sum of squares of differences in color between adjacent pixels. The image is constructed dividing the field into 16x16 squares of 256x256 pixels, each a gradient in red and green mapped on x and y. Blue is the same for each square and is sorted diagonally from 0 (top left) to 255 (bottom right). Odd squares are then flipped to minimize distances with adjacent squares. It can probably be improved with a better arrangement of the squares or by using rectangles in place of the squares.