Simply open the color palette on the right by clicking on the big square representing the current color. The color picker will be automatically activated. You can confirm that by the highlighted eyedropper icon on the left of this panel.
Hi -- thanks, but to clarify, I meant picking a color right from the drawn image. I believe it's Alt-click when using a mouse, but I usually don't have Alt when using the Windows 8 touch tablet.
philip : we didn't design BlackInk for touch screen.. but if we have a lot of user who have one we will try to think about solutions and features for it..