Dead cells are present on your face

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Your black because the skin has a pigment called as melanin and that pigment would be release more and more when you are in the sunlight for more time. so this pigment would become dark and it protects the internal parts of our skin. there is nothing like your black it is just that you have more amount of melanin in your skin and it is produced more.  
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What sink
Do u mean skin ?
sry ya I did not observe it