>Are the colours you're seeing very different, or nearly the same but noticeably different?
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>If the latter, monitor make and model, and adjustments can make that kind of difference. These days LCD panels typically have tons of available adjustments beyond the basic brightness and contrast, e.g. PC or AV modes, themes such as "Warm", "Cool" which bring out reds and blues in particular. It's also usually possible to individually adjust the individual RGB levels. Users with colour deficiencies or blindness may have radically adjusted these values.
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>This can vary even by time of day. There has been some recent evidence that too much blue light late in the evening can make it hard to sleep. I believe Apple already offers an option ("Night Shift") to turn down the blue in monitors after some user-defined time in the evening, it would not surprise me if Windows and/or monitor makers follow suit.

I've inherited a little laptop with XP on it, which had an app doing that kind of coloring, at least eight years ago.