Colour Label
A coloured tag applied to a file to indicate its status in a workflow, independently of its quality rating.
In depth
Because labels are orthogonal to ratings, they can track process rather than merit: red for needing retouching, yellow for sent to client, green for approved. The system only works if the meanings are written down, since the colours themselves carry no inherent significance.
Examples in practice
Green labels mark the frames a client has approved, while their star ratings still record the photographer's own judgement.