I colored each element of the robot separately. That is to say, I divided the robot into materials: gold, copper, silver, chromate, etc. This was to keep a consistent look throughout the eclectic mix of materials that the robot is composed of. There's also painted items, which have an appropriately worn, chipped look to them. Also, I made certain elements pop out more to keep the drawing from looking flat (this was done with shading). The final image has a blur filter over it to show movement. Effects like smoke, light and sparks were done over the main image. I named the robot to give him a little more character.