As stated in the manual, you can’t change GUI controls in Textadept itself. If you want to change the statusbar color, you have to modify a resource file where GTK+ reads how to draw various elements of the interface. The file to modify depends on your platform:

• on Linux: ~/.gtkrc-2.0 (create it if needed -- the location can also depend on your distro);
• on Windows: textadept-install-folder\share\themes\MS-Windows\gtk-2.0\gtkrc;
• on macOS: Textadept.app/Contents/Resources/share/themes/Gnome-Cupertino/gtk-2.0/gtkrc.

In this file, paste these lines (obviously replacing “FFFFFF” with the color of your choice):

style "custombg" { bg[NORMAL] = "#FFFFFF" }
widget "textadept*" style "custombg"

Note that the color name is not in RGB but in BGR!

Unfortunately there’s no way to change only the statusbar background color: we can only change the backround color af the whole window. You need to restart Textadept for the change to take effect, the reset() command is not enough in that case.

Note that this is only for GTK+ 2.

For Windows and macOS, since we modify a Textadept resource file, this has to be repeated after each update.