Egads, I fail at doing anything in a timely manner online.
I love this minimalist work. People seem to think that more detail automatically makes something awesome, but that is far from true and these lovely little pieces really prove the point.
You use nice blocks of color that do a wonderful job of suggesting the form and don't get sucked into using plain lines, even with the thinner elements.
I would watch some of your shapes and angles on the tack. I know driving isn't your thing, but even from an aesthetic point of view the vaguely teardrop shape of the collar would work a little better, allowing the eye to drop and move to the lower right without the help of the circular composition. The collar shape also tends to be straight towards the front and curved towards the shoulder.
The collar should also settle about parallel to he shoulder, which in an ideal world isn't much greater than 45 degrees.
That said I really do love this depiction of Wald. You did a good job on him.