Open the color image you wish to convert. Click "Adjust," then click "Hue and Saturation," then "Hue/Saturation/Lightness." You will see the "Hue/Saturation/Lightness" control window pop up. Adjust the hue slider all the way to the right for a setting of 180. Adjust the saturation slider all the way down for a setting of -100.
Ensure that the lightness slider is set at exactly zero (in the center), then click "OK" to complete the conversion.