I get question in my class almost every session:
I take a photo near the beach and the subject's face is too dark! Why is that the case when it is so bright out?!
Your camera is adjusting and reading the exposure of the background which, esp at a beach, is very bright and has a lot of light. There are a few things you can do to avoid this:
1- use a flash. If you use a fill flash you will light up the subjects face while still having the correct exposure for the background. If you don't you will either have a blown out background or a dark subject!
2- have the subject face the sun...This will work well if they are wearing sunglasses :)