Change the new "Hue/Saturation" adjustment layer's blending mode to "Color." You can do this by going up to the blending mode field, near the top of the "Layers" palette and left-click the down arrow and scroll down and left click "Color."



Create another "Hue/Saturation" adjustment layer and double-click on the layer icon. The layer icon is a scaled down image representation of the layer.

A "Hue/Saturation" dialog box for the layer pops up. Totally desaturate your image by dragging the "Saturation" slider all the way to the left or enter -100.



The image is now black and white, but you may want to fine tune it a little. Double-click on the layer icon of the first "Hue/Saturation" layer, "Hue/Saturation 1." Mess around with the "Hue" and "Saturation" sliders until your are happy with the results.



You can selectively make Hue and Saturation adjustments to specific color groups, like "Greens" by going up to the "Edit" field at the top of the "Hue/Saturation" dialog box and selecting the color group you want to selectively adjust.



You can see your adjustment in color by turning off the visibility of the second "Hue/Saturation" layer, "Hue/Saturation 2." To turn off the visibility of a layer, click on the eye icon to the left of the layer.