I found this absolutely brilliant!
This portrait of a stunning redhead was done by Samuel Silva, a lawyer and self-taught artist from Portugal. Silva used 6 colored Bic ballpoint pens to make this 8” x 9” drawing. By crosshatching the strokes of just the 6 different colors in layers, Silva was able to create the illusion of blending, as well as the illusion of subtle shades of new colors on paper.
You can check out more of his works on his DeviantArt profile.