Is it possible to move the mouse by one pixel on a retina display? I was trying to use DigitalColor Meter to find the color of a pixel on my retina MacBook Pro, but I found that it was impossible to get the color that I wanted because the smallest that I could move the mouse by was two pixels (in either direction).  If you zoom in using the control-scroll trick and disable pixel antialiasing (in the Accessibility preferences), you'll also see that this is the case.

Is it possible to move the mouse by just one pixel on a retina display?  It seems like the ability to do so would make the mouse movement smoother.  I guess to solve my color problem, I could just take a screenshot and zoom in on that, but it's a lot of extra work.
No - the mouse is aligned on the "fake" size of the screen and not the true screen pixel grid in most cases.

The concept of a physical pixel and a display pixel is a distinct one on retina displays since the hardware reports movements on a resolution-independant scale.

Furthermore, there appear to be some subtle bugs in the code side of things so even if the developer wanted to determine the next pixel's color it appears the routine that reports mouse position doesn't count physical pixels on this model screen.

There is a nice, very technical article by one of the programmers for Xscope - Retina for Masochists/ that explains a bit how the resolution that the software is told to draw gets translated into the actual on screen pixels which is fixed.

As an aside - the Xscope program is free to try and puts the digital color meter to shame on many aspects of determining color and much, much more.