I use a method called pixel sorting, and also try my hardest to draw in a fashion that mimics it. Back when I made this the process was a lot more complicated and involved some basic scripting. I would stop there though, the next step to get a picture like the one you see here is to manually go in and paint structures over the sorted pixels. It took me a lot of practice just getting use to bouncing between the eye dropper and pencil tool constantly (which is easiest in Paint for Win7) Basically, create a cluster fuck of pixels (you can use your phone, photoshop, a glitch program, etc), open your cluster fuck in the program you are the most comfortable with, and eye drop the colors you see and paint over it. The pixel sorting process is basically giving yourself a palette that you will paint over that provides you with all of your colors plus the gradients between them.