Have you deleted your registry keys and run the D2VidTst.exe once again?
Backup first before you delete anything from registry...find
Computer\HKEY_CURRENT_USER\SOFTWARE\Blizzard Entertainment\Diablo II\VideoConfig - delete only VideoConfig
Computer\HKEY_CURRENT_USER\SOFTWARE\GLIDE3toOpenGL- delete only GLIDE3toOpenGL
Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Blizzard Entertainment\Diablo II\VideoConfig - delete only VideoConfig
Run D2VidTst.exe and choose video mode, also if you have set some glide settings save those as screenshots so you know what to change again.
But maybe it is just your gamma messed up so try this first:
C:\Users\"your user name"\AppData\Roaming\MedianXL\save
open preferences.json with text editor and find "legacy_gamma": 195, - change its value and see does it help.