That is because Library module works in Adobe RGB color space and Develop module works in ProPhoto RGB color space.
Would suggest you to calibrate your monitor : http://www.lightroomqueen.com/articles-page/how-do-i-change-my-monitor-profile-to-check-wh ether-its-corrupted/
Also, if you have Lightroom 6/CC, try to turn off graphics processor under Lightroom Preferences> Performance
that totally worked, thank you!!
In fact, this means that you need to calibrate your monitor.