Quite often some parts of a photo require a saturation adjustment while others do not. If we increase the saturation globally, the most saturated parts get oversaturated and if we decrease it, the less saturated parts get undersaturated.
We need a Saturation Mask based on the individual pixel saturation in order to adjust it just where it is needed. Unfortunately even Photoshop does not provide a fast and straightforward way to create a saturation mask, like it does for brightness masks.
So this plugn, Selective Saturation, lets the user define a Saturation Zone by setting it's center and range with two sliders.
A mask preview mode is available to fine tune the settings.
Then every saturation adjustment affects only those parts of the photo with saturation value that lies in the specified saturation zone.
The "Smooth Adjustment" checkbox, when checked, gives a smoother adhustment by applying the full adjustment at the center of the saturation zone, while fading it to zero towards the zone ends.

If we increase the saturation globally, reds and some yellows get oversaturated: