1. Open a photo of an eye.

Eye colour 1

2. Choose the Magnetic Lasso Tool and select Around the eye. Then right-click on your selection and choose Feather. By feathering you will keep the color from flooding over the sides of the selection. If you have a high resolution photo, set the value somewhere around 10. If not, set a smaller value.

Eye colour 2

3. After you feathered the selection, you go on to the final part which is changing the color. You can either go to Image -> Adjustments -> Color balance or Hue/Saturation. Move the bars until you’re happy with the result, click OK, and it’s finished.

Eye colour 3