Brown pigmentation on the shins and and, in general, form the mid calf down is usually due to chronic venous insufficiency and resultant stasis of the veins leading to hyperpigmentation. The first step would be to have a full venous evaluation with a venous reflux ultrasound. If you have venous reflux (malfunctioning valves) then these should be closed first to arrest the progression of the problem. Following this, there are creams that can be tried but usually the discoloration will only slightly improve and not resolve. The other important thing to do is to make sure that there are no spider veins in this area contributing to the discoloration. If present, these can be treated with sclerotherapy to lighten the area.