A tutorial on how to change the colour of a person’s eyes in a portrait shot in Photoshop
Create a new layer and change its blend mode to Hue. Select the Brush tool with 100% Opacity and set its size so that it’s just large enough to cover the colour part of the eye.
Click on the Foreground swatch to open the Color Picker menu. Select a new colour for the eyes, such as orange (this doesn’t have to be a natural colour!).
Zoom in close to the eye and brush over the colour part of the eye with 100% opacity. Lower the opacity of the brush to 40% to add colour at the edges.
If at any stage you went over the edges, use the Eraser tool with 0% Hardness to remove those areas of colour on that layer.