To make a color splash video, open your clip above: this page starts on the Red Splash look, which keeps reds and turns every other colour grey. To keep a different colour, open Pro tools (P), go to the HSL tab, choose the band you want (Orange, Yellow, Green, Aqua, Blue, Purple or Magenta) and switch on Keep only this colour. The Colour splash category in All looks has more ready-made versions to try.
Selective colour, as it is also called, works best when the colour you keep belongs to one subject and nothing else in the shot. The tool chooses pixels by hue, not by outline, so a red bus in the background survives along with the red coat in front. The sections below cover choosing a clip that suits the effect and keeping the edges steady. For a fully grey version, see black and white video.