That, or you can go to Tools > Script Editor > Scene_MenuBase
Look for this line:
#--------------------------------------------------------------------------
# * Create Background
#--------------------------------------------------------------------------
def create_background
@background_sprite = Sprite.new
@background_sprite.bitmap = SceneManager.background_bitmap
@background_sprite.color.set(16, 16, 16, 255)
end
And switch the 160 (default) to 255 as above.