Oh! I got it, Thanks a lot!
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https://bugs.launchpad.net/bugs/1928294
Title:
gamma adjustment not working
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Public bug reported:
Used "xgamma -gamma" but it's not changing the gamma value although it's
executing successfully. The gamma value is remaining the same as it's
been before. The same problem is persisting with "xrandr".
ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: xorg 1:7.7+22ubuntu1
