The notion of ‘normal’ is part of our collective conscious. We, as a group of people tend to believe that there are certain things which are good and superior as compared to the others we refer to as ‘bad’ which is akin to ugly and inferior. Color of skin is one of those areas where human race has over the centuries developed a pattern of thinking with hatred towards black as its integral part.
It all started and took pace with the advent of colonialism. The old trade routes in the seas (mostly) were the domain of Arab traders who monopolised this trade from far off Malay islands to China and then to the Mediterranian countries and Europe. Silk, spices and gemstones plus food grains were traded all over the Europe and Asia. The workers on the ships were black Africans who were famous for their built and were hardworking. But in those days discrimination was not a part of civilisation as Arabs by virtue of their code of ethics, Islam, were forbidden to discriminate between people on account of the color of skin. A black labourer enjoyed the same rights and privelages as a fair skinned arab counterpart. This was true of the society in general and we are talking of the ‘dark ages’ of Europe (7th century A.D. to 15th Century A.D). The Dutch, The Portugese and The French were being industrialised after the renaissance and workforce was needed. For the produce of those industrial empires a larger consumer population was vital as well. The colonisation had begun. First the African and then the ‘crown of the British empire’, India were colonised by these naval forces of the world. They replaced the Arab traders and superior technological advances helped them in achieving this target. The white man of Europe when confronted with the ‘illiterate’ dark skinned native of Africa or Asia immediately felt ‘superior’ to him and developed a superiority complex (read hatred). He needed this hatred to ruthlessly rule over the colonies. French, Dutch, English and Portugese colonies spreaded and by the beginning of world wars most of the Africa and Asia were divided among these powers. They have developed a lavish lifestyle (in contemporary history you can look at the slave trade by Americans and how the blacks were hated for a long time, and even now there are sporadic incidences where it is tried to prove that black-is-inferior).
These powers have the white-man-complex which gradually became an inherited trait and to this day continues to affect our minds and cloud our thinking about darker shades of skin.
Had it not been due to world wars, incidentally, larger parts of Africa and Asia would not have been independent states even today.