Colour grading is one of the final stages of Post-Production. Colour grading is the process of manipulating the colours in a shot to match each other and the tone of your video. Where professional editors edit videos, professional colourists colour the footage.
When you film videos on your phone, the colours likely look bright and saturated because they are being recorded in a linear colour space. When you film on professional cinema cameras, instead of filming in a linear colour space, you film in a logarithmic colour space (LOG).
When filming in LOG, the camera sensor is able to capture more colour and luminance information. This results in a very flat, desaturated image out of the camera, but contains a lot of colour information. It is then a colourists job to colour grade the footage to add contrast and saturation.
The reason why professionals use this workflow is because it allows you to have more control over the final image, because there is more information in the image.
At Story Ninety-Four, we colour grade our footage in the industry standard colour grading software DaVinci Resolve.