Colour range describes how numerical signal values are assigned to visible brightness and colour information in a particular arrangement. Source and display interpretations need to agree. A mismatch can crush dark detail, clip bright areas or make blacks look grey, even when resolution, bitrate and network delivery are otherwise behaving correctly during playback.
A practical example
A computer outputting one range to a television expecting another can make an ordinary desktop or video appear washed out. Correctly matching the supported settings addresses interpretation of the signal rather than requesting a higher-quality stream from the service.
A common misunderstanding
Avoid compensating for a range mismatch only with brightness controls. That can obscure the cause and spoil other sources that already use matching output and display arrangements.
Related terms
Stable technical definition. Editorial approach