Your balls are on the outside because they need to be a couple of degrees lower than your normal body temperature to stay healthy. That's why we have to go through all the trouble of having them swinging around whereas women have their equivalents bits inside.
The skin on your penis is pretty thin and gets very little light. It'll burn very easily (Just like when you get your chest out for the first time in summer when it's been under jumpers all winter).
Sun tans are actually a preventative measure your body takes to save your innards from the roasting of the sun, similar to how a blister is there to save the skin underneath: it's not a healthy thing at all. Further: get out in the sun and stop being a girl using sunbeds.