Well, if you are talking about a shooting stage they are generally black (to cut down on uncontrolled light and reflection), when they are treated at all. Many sound stages are fairly generic, come-as-they-are big warehouse type spaces. More established ones tend to be finish out more. In those cases ceilings tend to be black.
If you are talking about an editing room, they vary according to taste. We have ours painted dark to cut down on ambient light glare on the monitors. There are varying, strong opinions about edit suite paint schemes and how they affect the subjective judgement of color balance and luminance values.
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