Jet
You mean to take a photo like this.
And do something like this.
Here is how I do it.
Open the photo
Using the Brush effect.. Size 128 .. Tint Black at 100 Opacity
Using the Brush effect.. Normal .. I like the effects of using "Normal" better than "Colorize". Choose the color that you wish to make the object.
It helps to zoom the photo to show as much of the object that you wish to color in the window as possible once tinted to the desired color or effect.
Adjust the Brush size to inside of the smallest part of the object.
Adjust the Opacity to around 20% to start. If it does give the desired depth/color tint. Move up the Opacity 5% until you get the effect you are looking for.
Ctrl and Z at the same time will undo what you just did.
Once you start. Try not to stop the brush until finished. For each overlapped brush stroke will make the overlap darker.
I like to use a feathered brush. Which on my program is the third and forth bursh from the top left of the "bush chooser window" as DD calls it.
Hope that it helps you somewhat. I put it as simple as I could in hopes that it would be easy to follow the steps.
Remember Ctrl + Z = Mistakes undone.
Another little tip. When you first open a photo. Hit File, Save As and add something to the end of the photo, Hit Save. That way you will have of the same photo. The orignal and the one that you are working on to use for comparing the org to the new.
Example are the photos above. One named "Piggy" the other "Piggy3333" or something like that.