This photograph was snapped just at the twilight of sunset. The red color channel was isolated from other colors.
I isolated the red color channel in this black and white photo of the Golden Gate Bridge at night.
I set my camera for long exposure, and amused myself by tinkering with some of the camera settings. In this mode, everything appears desaturated except for red colors. Image was captured from the Marin Headlands.
I got lucky! No tripod, using the pole barriers and listening carefully to a photography teacher instructing his students.