On what basis is the skin colour in humans considered polygenic ?

Skin colour in man is controlled by

Skin colour in humans is an example of

In frog the skin colour is due to

Urine colour in healthy human is

In a cross between negro and albino skin colour of humans showing polygenic inheritance, the phenotypic ratio in F_(2) generation will be

Whose skin colour does not change

Inheritance of skin colour in humans in an example of :-

How many alleles determine the skin colour in human beings?