With PS, you can change the color of your images to have a different color motif, which can help if you found a certain image you like but it doesnt matches your general idea for a page or anything of that sort.
First Step, would be to of course open PS along with the image you wish to colorize - I chose this one of an Iris, and will go with you along the way.
Now, press CTRL+U and it should open to you a window titled Hue/Saturation. Tick the Colorize tab at the bottom right corner, the colors of your picture should immdiately change into a different color scheme.
The next step would be to fuss around with the Hue, Saturation and Lightness options until you will find the picture is to your liking.
Hue: Changes the color scheme
Saturation: Changes the light focus
Lightness: Makes your image darker/brighter
Once you're satisfied with your image, click OK and there you have it - a whole new color for your old picture!