anchor.diff:  http://deepsymmetry.org/afterglow/doc/afterglow.show.html#var-add-midi-control-to-cue-mapping[afterglow.show/add-midi-control-to-cue-mapping].
   
   |`:variables`
  +|none
   
   |Specifies a sequence of show variable bindings that
   can be used by the cue's effect. Each variable specification is a map,
  
positive.code: alone.
  
  |`:priority`
  
  |Sets the effect priority used when adding the cue's effect to the
  show. This can be used to make sure the effect runs before or after
  
negative.code: long or not informative enough.
  
  |`:color`
  |white
  
  |Sets the color of the cue within the grid for hinting about its
  purpose and relatedness to other cues, to help operators learn and
  