My arms are so much darker than the rest of my body, it's so weird!?

My arms are so much darker than every other part of my body! My skin is very fair, but my arms are quite tan! I have keratosis pilaris on my arms, could that be the cause of the tan on my arms? How can I get rid of it? I DO NOT like tanning and I always wear sunblock so I don't tan, and I hate having dark arms, light shoulders, and light hands, plus a light face and etc! It just doesn't make sense, I really hate my arms since my KP is so bad, so I almost always keep them covered up... how could they be so dark?