Change Photo Black and White Except Features in Photoshop?

I have seen pictures before where the whole thing is black and white except certain parts. For example there will be a picture of a lady and the whole thing is black and white except her lips and eyes will still have color. This gives a really cool effect because it really exentuates these features. Anybody know how to do this in photoshop, im sure it has to do with masking but cant figure it out.Change Photo Black and White Except Features in Photoshop?
Select the area you want to retain color details.

Invert your selection

Apply gray effect.

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