Make one color the only color in a clip: a red coat in a gray street, a yellow taxi, a green umbrella. Everything outside the chosen hue loses its saturation, while the matching areas keep theirs.
Choosing the color
Pick the Keep Color from the object’s midtones rather than its highlight or shadow, because those drift toward white and black. Tolerance widens the range of hues that count as a match. Start around 20% and raise it until the object is solid in both its lit and shaded sides.
Background desaturation
At 100% the background turns fully gray. Lower values leave a trace of the original colors, which looks less like a cutout. Other objects of a similar hue survive too, so a red sign behind a red coat stays red.
Footage that works
Color splash works best when the kept color appears nowhere else in the shot. Skin tones sit close to reds and oranges, so a red subject near faces often brings the faces along. Shift the Keep Color slightly toward magenta or narrow the tolerance to separate them.