The two center Xs are the same color - both gray!
Thanks to Prof. Michael Bach, I'm able to provide proper attribution: It's from R. Beau Lotto at http://www.lottolab.org/Visual%20Demos/Demo%2024.html
also referenced on http://www.purveslab.net/
Battle scene (?Kunisada)
Figure with falcon
Men with elephant
Ancient Japanese Grave