Place the reference photo on your work surface. Draw around the dark areas and the light, creating a line between the two using the pen. This will create an outline with stark contrast between the darks and the lights.
Measure the length and the width of the canvas, and divide it in to even grids. Apply the same grid to the reference photo, scaling down, if need be.
Transfer the lines from the reference photo to the canvas, in correspondence to the grids on each.
Paint one of the colors in the areas where there is dark shading, as defined by the lines. Reference the photo to re-establish where these are.
Paint the other color in the light areas, as defined by the lines. This will create a striking portrait, as the colors will be complementary to each other.