Copic multiliners, Copic warm and cool grey Markers on 2 ply Strathmore bristol. I was originally only going to do it as a black and white ink drawing but I just got started and didn't stop until I was done.
What I did was color it the way you do a water color. Keep in mind that these are all grey tones but warm and cool greys, not Neutral grey. It creates a desaturated color effect. I laid all the flat tones first and then applied the shadows. I started with the lightest possible base for each color and built them gradually creating shadow and highlights.