The author Alice Walker was first credited with using the word in an 1983 essay essay entitled "In Search of our Mothers Gardens" and she described colorism thus " “prejudicial or preferential treatment of same-race people based solely on their color.” In essence the term describes a person who is of the same race, lets say for arguments sake that they are of Brazilian origin. Now, for anyone who has been to Brazil or knows many Brazilians will tell you that people who identify as Brazilian come in many different skin tones and yet 68.3% of Brazilians believe that their race has an impact on their daily lives. This impact is seen in many aspects of life that we might attribute racism to except that the people involved are not, necessarily, of a different race, they simply have a different skin tone and thus are judged or treated unfairly or biased.
It is very similar to Racism and I pray that one day soon we will live in world where it doesn't exist. Where a person will be judges solely on who they are and not what they are.