Disclaimer: I don't own Naruto.
I. Sketchpad
Sai was born as a sketch. Unfinished, unstarted - whatever he was, it was nowhere near done. A rough outline of what he might, someday, be, that was all. He was all wavering, crude, pencil lines, in everything he did - from the too stiff, too hard way he walked at times, to the smooth, almost floating gait he used at others. Indeed, Sai in the beginning was inconsistent, and nothing more than a rough copy.
II. Ink
Sai inked himself with deepest black. Bold strokes - he had to cut a path in the world, to become something finite, whatever it was, instead of just flip-flopping all over the place. So he outlined himself in darkness, wrapped impenetrable barriers of flowing, permanent ink around himself and refused to move, and left the rest bone white.
III. A Wash Of Colour
And finally he added colour. This came slowly, gently filling in, almost unnoticeable, at times, or crassly bursting through at others. It was a long time, full of uncomfortable shades and unreasonable shadows cast in all the wrong places, stopping him from being the way he should be and making him something else instead. Some colours were easier than others - easier to loosen his reigns and let the brilliant reds charge in than it was to wash himself with soft light and tender care.
IV. Framed
Sai didn't think he'd ever finish himself. It was true what they say - you're your own worst critic, and when he examined himself, all he could ever see were the flaws, tiny but pervasive, in his bland countenance. No matter how many times he'd hear it, whispered behind his back - "look at the dull boy, see how perfect he is, pretty as a picture," - he only ever saw the screw ups. But maybe that was alright, because at last, Sai was ready for the world to see, unfinished or not. Like they said, pretty as a picture.