What is meant by a blue shift and a red shift for light? An approaching source of red light gets brighter, making a red shift in color. A receding source makes blue light brighter, resulting in a blue shift in color. An approaching source has increased light frequency - a blue shift. A receding source has a decreasing frequency - a red shift. In an approaching source, blue light shifts to green. In a receding source, red light also shifts toward green. A receding source has increased light frequency toward the blue end of the spectrum, whereas an approaching source has a red shift