iMac screen not displaying all colors?

Question

macOS

I noticed such a problem on a home iMac 2009 that some colors simply do not appear. For example, a block on the page has a gray background (#f7f5f2), but on the screen it is white. Or the block has a gray one-pixel frame

that I see only in the place where the shadow from the window falls on it.
What is it - the monitor dies or some kind of calibration is needed?
I tried to change the profiles and the calibration procedure in the System Preferences (Monitors › Color) - it does not help.

Answer 1

Of course, calibration is needed, any monitor needs it. Most likely your brightness is turned up. I perfectly see a gray stripe in your picture on a macbook with a calibrated monitor.

Answer 2

I have the same thing on an old imac, and so far I have not come up with an explanation for this ...