Subungual melanoma: nail bed discoloration or nail plate? My nail plate has a horizontal band 1/2cm across but skin underneath is normal. Confused

See a doctor. Your nail needs to be examined by your doctor, preferably by a dermatologist. After examination you will be guided further. A close watch for change in the size of discoloration or the skin around will guide the doctor further. Keep good photographs to detect changes over time(weekly). Good luck.