Whenever Arrows or Shift+Arrows key are used to quickly increment the value in a field in th Color panel, without GPU (or with Overprint Preview, which is done with CPU), — the color does not get updated on canvas, while in 26.x version it works just fine.
The CPU canvas now gets updated only when Tab or Enter get pressed. Pressing an arrow key, with or without a modifier, is a finite operation, and should trigger the redraw event too!