Digital Light & Color

In Colour Zones, even if the Auto Preview is off, adjustment to the mask sliders causes instant recalculations, which makes it hard to set the sliders to the right positions (which I know more or less after probing the image).

It looks like it is only recomputing the histograms and not the entire transformation -- something similar happens in some other transformations as well. It does this in case you change the Amount settings which in turn can affect the histogram.