Final answer:
To make the iris appear deeper, use a darker eye color shade, as darker shades can enhance the perception of depth.
Step-by-step explanation:
To make the iris appear deeper, use an eye color shade that is darker. When adding black to a hue, you create a shade, which can give the impression of depth or recede, making the iris stand out more. This is analogous to the way the pupil expands in dim light to gather more light, indicating how darker colors can enhance the perception of depth in the eye. The iris, which adjusts the amount of light entering the eye through the pupil, alongside other structures like the cornea and the retina, work together to process light and contribute to our visual experience.