Objective: changing the default theme that comes with TexStudio to a darker theme that appears more comfortable for your eyes.
Procedure
Go to your TexStudio settings directory:
For Linux/Unix/Mac: ~/.config/texstudio/
For Windows: %APPDATA%\texstudio\
In TexStudio, click Options -> Save Profile and save your existing profile under a new name (e.g. newtheme.txsprofile) in the above settings directory.
Open the file (i.e. newtheme.txsprofile) with a text reader and scroll down until you see the following. Delete all lines (if any) under [formats] leaving only the first line “version=1.0”.
Replace the (deleted) lines with my text hereand save the file.
Go to Options -> Load Profile and select the “new_theme.txsprofile” file you saved earlier.
Exit TexStudio and reload. You should be seeing the new theme now.
Fine-tuning the color scheme: you can modify certain colors by going to Options > Configure TeXstudio > Syntax Highlighting