What Causes Skin To Get Mottled And Pale?

the skin on my lower legs has become mottled . There are areas that do not sun tan, but stay pale, next to those areas the skin gets dark, but it s splotchy. What would cause the skin to suntan unevenly, & just on the lower leg area? We are on vac. in FL & are in the sun a lot. I am 59 yrs. old.