This should be entitled, "Kim, why are you teeth so fricken yellow?", especially since I don't drink pop or coffee, but I will put myself out there for the sake of teaching Photoshop. How my beautiful, red headed, sister-in-law has such white teeth when she drinks coffee and pop is beyond me.
Let's look at three different methods, and then we can decide which one does the best job. Here is the original shot:
Some tips before we get started:
Always make a duplicate first, cuz we all make mistakes.
If you want to see the original image next to the one you are working, on so you can get a better feel for the changes, go to View>New View. Put both views next to each other so you can see them at the same time.
To hide the selection box (or the marching ants) click Ctrl-H
The first thing you should do for every step is to zoom in so the teeth fill the screen, aren't they lovely. Use the magnetic lasso tool to select around the teeth (This tool can be found in the tools box, second one down under lasso, click it and you should see the magnetic lasso tool.)
Let's try the Hue/Saturation method. With the teeth selected, go to Image>Adjustments>Hue/Saturation. Now click the box that says Master and change it to Yellow. Then, turn down the saturation slider as much as you think is needed. Zoom back out to see what it looks like.
Here are the results:
Here is another take on that method. With the teeth selected, go to the layers box and add a Hue/Saturation Adjustment Layer, like so:
With master selected turn the saturation to -18, and the lightness to +18.
Changing the option to yellow, put the saturation at -100 and the lightness at +32.
Hit OK, zoom out, and check out the results:
Next, let's try the Selective Color Method. Go to Image>Adjustment>Selective Color. Change the drop down selection to yellow, and move the yellow slider to the left until you are happy with the color.
Zoom back out and check out the results:
The final technique is the Dodge Method. With the teeth selective pick the dodge tool (this is the one that looks like a black magnifying glass). In the top options pallete change the exposure to 20% and make sure it is set to midtones. Set the brush to a round, feathered brush that is bigger than the selection. Make one pass over the teeth and check out the results. Keep doing this until you are happy with the colors. Here are the results:
I prefer the Hue/Saturation Layer Method. It brightens the teeth, but still looks natural. Each person has their own preference, though. Which one do you like?