If the image is in RGB, look at the individule channels in BW and select the lightest channel as the only active channel. From the keyboard or the select menu, select the full canvas (select all) and then copy the channel to the clip board. Create a new RGB doc. The size will be (by default) exactly the size of what is in the clip board (original doc). Paste the contents of the clip board into the new doc and flatten it. It will be a perfect bw image of the channel you selected from the original. Use the curves palette to adjust the area of concern with out worrying about the rest of the picture. Once satisfied with the lightness or darkness of the pic you can begin to colorize it. Tip: With the curves pallette open you can click and drag across the area of concern and it will appear in the curves pallete as a sliding circle that will show you exactly the area of the curve that will need to be adjusted.
The easiest way to colorize the image from here would be to use the Hue Saturation command. Check the colorize check box and then adjust the Hue and Saturation sliders until you have achieved the desired color. Duplicate the base layer and then set the duped layer to color blending mode. You can then use the dodge and burn tools to manipulate the colors to creat variation or you can pick colors from the color picker and airbrush to make subtle variation changes in the color. Once satisfied, you can select the area of interest by using the pen tool or by other means and then put it back into your original document. You can make further adjustments to the corrected area or the surrounding areas to complete the effect. It will depend on the lighting and orientation of the original. Without seeing exactly what you have, this is the best that I can offer.
Hope this is Helpfull
Jerry
PS: Note to Eve...No
