In the Painting Skin Color Base video, you mentioned there wasn't a way to use the color picker... can't you just hover over the color swatch and press E and then using the color picker from any panel within the Blender Window?
Image Editor has some modes to choose from, View, Paint or Mask. While the color picker doesn't work in View mode it works in Paint mode. You can open the reference image, change to Paint mode and the S shortcut for color picker will work. Just try not to paint over your reference.
I see what you're saying... can't sample from a shortcut... and I guess what I was asking about is essentially just the shortcut of what he did :D