Hi, this is a simple tutorial. Basically what it is: A grey-scale image, with one colored part.

1. Grab a simple image, I used an Eye, This is a great way to start, nice and easy. you can use my image if you wish:

2. Press Ctrl + U then click colorize then put it to 0, 0 and 0. This should make it go grey-scale.

3. Grab your Lasso tool

and zoom in, Trace around the Iris (the middle of the eye).

4. When you let go, it will automatically connect it back to the start and make a selection. Go into the colorize menu again (CTRL + U). Tick colorize and set saturation to 50. next choose a Hue that suits you. i chose a green colour:

There you have it, Nice effect. Use it on other images, Such as a hand with a ring!