If you're swimming the full sun in a pool, we would recommend the dark grey mirror. This is the darkest of the tints.
If you're swimming in the full sun in open water, we would recommend the dark vermillion mirror. It is dark enough to shield your eyes but also light enough to be able to see the water. Cobalt is also ideal for open water swimming.
You can learn more about our goggles and color tints, here.