Color cast
Also known as: colour cast, tint
An unwanted tint across a whole image, usually from the wrong white balance or from light bouncing off something coloured nearby.
Updated
What it means
A cast is a bias, not a brightness problem. Everything in the frame leans the same way, so neutrals stop being neutral and skin goes with them. The eye forgives a dark clip and refuses a green one.
The usual cause is White balance left on automatic. A camera guessing from frame to frame gives green under trees, blue in shade and a different answer every clip.
Environments add their own. Water throws cyan upward, snow reflects the sky, and a Polarizing filter (CPL) changes the balance again depending on its angle, which is why two clips from one beach can disagree.
How it works in practice
Fixing it starts with a known neutral. A grey rock, a white jersey or a cloud gives a reference, and Color correction against that reference beats adjusting by eye.
Preventing it is simpler. A fixed value chosen for the conditions keeps every clip of the session consistent, and consistency matters more than being exactly right. One wrong value is a single correction; twelve are twelve.
Scopes are what make the judgement reliable. A screen adapts within moments; a Histogram or a vectorscope does not, which is why a cast is measured rather than eyeballed. Trusting the monitor is how a cast survives a grade.
What to watch out for
Underwater footage is the hard case. Red disappears with depth, so what looks like a cast is missing information, and a Red filter at the time of shooting does what no grade can.
Casts also differ per camera. Two bodies in one session can lean opposite ways, and Color matching has to remove both before the look is decided.
Mixed lighting cannot be fixed globally. A rider in sun against a shaded wall has two casts in one frame, and correcting one of them makes the other worse. A local adjustment is the only honest answer.
How RawClip handles it
Clips are brought into agreement while the sequence is assembled, so a green clip from under trees and a blue one from shade stop reading as two different recordings. Material shot with a fixed white balance needs less of that work and survives it better.