There is a csv file of color values and names in this project:
Take that file and reprocess it from 2 columns (color name, 32 bit color value) to 5 columns (color name, 8 bit red, 8 bit blue, 8 bit green, 8 bit transparency) for the next step.
Take your input color and break it down into 4 values (red,blue,green, transparency) .
Run through the 5 column list and compare each color against your sample, using your favorite metric (manhattan distance, pythagorean sum of squares, etc) and keep the color with the minimum distance against your sample color.