I believe the darker your skin tone, the more easily your skin tans. However, I have very fair skin yet my face and neck are still slightly darker (more red) than my body. I also think it's because the skin on your face is thinner and the blood shows through easily.
For starters, make sure that you use sunblock with at least SPF45 when you go out in the sun. At least this will help prevent further darkness. You may also consider using a hat to shade your face from the sun.