This is one of my least favorite images. My first thought was to just cover everything in black since there were the most squares of it. But doing the white I think is more tedious. So I would cover the entire thing in white to eliminate the 2's, then the black 1's won't be as annoying. The 3's aren't a big deal. But, personal preference. People might not like to take "shortcuts" by intentionally coloring the entire picture in one color to make it easier.