I have 2 easy ways for you to do this.

First, you need to open an image.



Next, go to Layer > New Adjustment Layer > Hue/Saturation.



A dialog box will show up. Just mess with the Hue slider until you see something you want.



There should be a layer mask filled with white on the Hue/Saturation layer. You need to fill it with black. Try Ctrl + i (Invert)



Now you need the brush tool and set your foreground color to white.



Start to brush where you want that color.



And here we have Dwayne Wade ready for St. Patrick's Day.




PT. 2

First, open your image. Then create a new layer and fill it with the color of your choice. Set the blending mode to color.



The entire picture color should change.



Add a mask to the color layer. (Button at bottom of layers pallette with a circle in a square)
It will be white, so press Ctrl + i and make it black.



Brush tool, white foreground.



Brush where you want the color.