Starting back at this point in the print progression:
I went on to add the outlines of the heads, this time in a dark gray. I used stencils, which caused the ink to "squish" out along the stencil edges as you can see here:
Then I added the energy swirl pattern on top for a different look:
Here are all four of the variations:
I don't like this version as well as I like the previous blue and yellow version, but I'm having fun experimenting no matter what the results.