By subject's request, I'm posting a portrait done in Illustrator. Took about 9 hours start to finish:
The reason it took that long is as below. Each blue line is a single pencil stroke, the hair so many strokes it became solid:
Now lest you think I did each color strand seperate, I didn't. To get the various tones, including the grey, I used gradients, matching each section of hair as the original showed.