How do I paint brush strokes with no color?

[Dan5E7B]

Using Photoshop CC.

How do I create a brush stroke effect without adding color?

I am painting already existing art.

The art already has color.

I want to create a brush stroke effect in the existing art, but I do not want to paint any color - just add a brush stroke effect.

How do I do this?

(I have searched but have found no answer)

[Chuck Uebele]

You can either use the mixer brush or paint on a separate layer and use luminosity, or spotlight as a blend mode.

[c.pfaffenbichler]

I guess to some extent even the Smudge Tool and the Art History Brush Tool could be used to simulate »painting strokes« on a photographs. 

[c.pfaffenbichler]

What do you mean by »brush stroke effect«? 

Please post an example and an image you want to edit thusly. 

[JJMack]

Blend in a layer that has a brush stroke texture that is netural gray then adjust the imag's  overall color.