R2-D2 is a classic astrodroid from the Star Wars universe. It features a gentle and friendly round body with a dome-shaped head. Its arms and legs are short and stubby and end with grippy, suction-like feet for help in navigating with organic and metal surfaces. Its predominantly blue body shows a white belly and is accented with shades of red and green, featuring a red and green eye, and a green panel on its head.
If you were adding color to this astrodroid, you could make it more vivid by doing a gradient of blues, starting with a light color at the head and darkening to a richer color at its bottom. The eyes and panels could be a deep contrasting red and green respectively, to help the robot stand out on the page. The white of the belly could be muted with a slightly off-white shade, to add a sense of realism. Above all, you can make R2-D2 your own creations by adding splashes of color anywhere you'd like!