How rare is gray/mostly light blue eyes and pitch-black hair/dark brown almost black hair? give detail on how and why? will give brainliest.

It's not that common actually quite rare because gray eyes are less than 1 percent of the earth population. Being that blue eyes and black hair is considered genetically impossible gray eyes are lighter, which makes it even more most likely impossible.  
Fun fact: 10,000 years ago blue eyes didn't exist they are a mutation and everyone with blue eyes is technically related.

the glands which are associated with each description is given below:

pancreas - is an endocrine and exocrine gland that secretes juices with enzymes for digestion. salivary glands- with protection and digestion in the mouth. liver- secretes bile for digestion.   lachrymal glands - secrete tears to moisten eyes and protect them from particles and infection.   sweat gland -regulates water, salt, and temperature. oil glands - to form a protective barrier on the skin.   goblet cells - secrete mucus for protection.