List the description of all the colors.
SELECT color_description FROM ref_colors
SELECT color_description FROM ref_colors
[{'color_description': 'red'}, {'color_description': 'green'}, {'color_description': 'yellow'}, {'color_description': 'blue'}, {'color_description': 'black'}, {'color_description': 'white'}, {'color_description': 'purple'}, {'color_description': 'gray'}]