Skin Discoloration In Left Leg Spreading To Right Leg, Weightloss. Healthy Lifestyle. Recommend

I have skin discoloration on my left leg and starting on my right leg. I do a lot of yard work and I don't lay in the sun or tanning beds . For the first time in my life , my legs ar extreamly dark. I 've had stomach problems the last few years which no dr. has diagnoized . I have been healthy for the past four mos. I am 65 years old I exercise and in between all this I am very healthy. I 've lost thirty lbs over the last one and half years. I am now concerned about my skin.