Click OK, the selection will automatically fill the associated mask. Change the blending mode to color (top of the layers window - says normal before being changed) and then press Control I to invert the created mask so that the light areas don't take the color and the dark areas do ...
You can change the brightness of your mask, with the the same brown Solid Color adjustment layer selected type Control-L to bring up Levels, play with the triangle sliders and watch how the mask on the adjustment layer changes and how it changes the color in your photo. In this case darken it a little by moving the middle triangle to the right some.
Now for more fun lets add a cross tone / duotone affect to exagerate the difference in color between the lighter and darker areas.
Select the background, type control-alt-~ again to select the luminosity, now create a new Solid Color adjustment layer, pick a very subtle almost grey blue or grey violet color, Click OK and change the blend mode to Color. Type control-I to Invert the mask. With this layer still selected type control-L to bring up levels - slide the middle tringle to the left some to lighten the mask.
Your final photo and layers window should look something like this ...
How this works -
Color blending mode only uses the color information from the Solid Color layer, the mask hides the color more where darker and less where lighter. The light cool-grey layer under the brown layer affects the lighter areas more, but is hidden where the top layer changes the color to brown. In both of the Solid Color adjustment layers the whites are protected from coloring by the masks so the final photo maintains a clean look.
Hope you like this technique as much as I do, Roger