It may look as if the two arms of the `X` use different shades of pink, but in fact the whole X only uses a single color.
Explanation
The difference is that one arm of the X consists of pink squares that replace white squares in the background. Thus these pink squares are surrounded by green squares. The other arm of the X also consists of pink squares, of an identical color, but in this case they replace green squares in the background, and are therefore surrounded by white squares.
Painters have long known that the way a color looks in a painting is affected not only by the actual shade of the colour itself, but also by the colors that surround it.
