I'm sure you must have used Hue/DSaturation umpteen times. If you use it as an Adjustment layer you can keep a portion of the image in monochrome while revealing the original colors in other parts of the image that you may want.
Here is a free stock image.
The same image after tweaks with a Hue/Saturation Adjustment Layer.
The tutorial is here
Other photoshop tutorials are here
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