Add a new column to a data frame of gradient color based on a specific column of the data frame
colorize(df, col.att, color, new.col.name)a data frame
an integer indicating the column with which to create the gradient
a character vector of length two indicating the starting point of the gradient and the ending point of the gradiant
a string indicating the gradient column name added to argument df
a data frame.
argument df with an additional column corresponding to the gradient column based on argument att.