White Spaces and Unknown Unknowns

I dug up some coloring books from the basement's collection of arts and crafts supplies dating from when my kids were growing up.  I needed something to occupy my hands and empty my brain.  Ironically, that tends to be when ideas show up unexpectedly.  

I was attacking my third drawing when suddenly the decision I had to make wasn't which color marker to pick, but whether or not to color the "white space".  The pre-printed lines clearly show shapes and the brain immediately interprets the area between lines as something to be colored.  This happens even with geometric shapes or lines that don't represent a recognizable object.  Of course, one could decide to leave some of those shapes uncolored, but that means they are intentionally left white.  What I was wondering about was whether or not to color the white space that corresponds to "empty space" or negative space.  

In cognitive science, this relates to selective attention.  Our brain focuses on certain stimuli while ignoring others.  We notice some things and miss others.  Refocusing my attention to the empty spaces was a way to alter my focus and consequently, my perception of the image I was coloring.  I refocused on the negative space. This is somewhat similar to or related to the concept of unknown unknowns, the things we don't know we don't know.  We're oblivious to our own blindness and ignorance.  

What am I not seeing?  What am I missing?  How could I see differently?