My dad has diabetes his legs are all chapped and getting dark. is this serious?

See your doctor: Lots of diabetics have weak veins which can cause stasis dermatitis and weeping ulcers. This is a benign condition and we typically use compression stockings. Other things to consider include cellulitis (skin infection) and most importantly peripheral vascular disease (blockage of leg arteries). Infection and pvd can be serious. I would recommend having him see the dr. to diagnose it asap.