When setting the background color of the gantt chart, it does not appear to apply to the list of activities.
In Options>Gantt Chart>Colours>Background you can set the "Working Time" background colour, which can appear to change the entire Gantt Chart background when you are zoomed out, but if you zoom in you will notice that the non-working time is coloured differently according to your settings. You are correct that the options on this page affect only the right side Gantt Chart, not the left side Task List
Currently there is no setting to change the background colour of the entire Task List.
An option to colour the task list is a good suggestion that we will consider for a future release.
There is a workaround: Switch to Gantt Mode>List. Select All tasks visible, right click and choose "Change Colour". Deselect "Default" and then pick a colour. This will affect the left and right side for selected tasks, but not new tasks that are added. However, when you zoom in on the Gantt chart, you will no longer be able to see non-working time as a different colour. This would be best done after the schedule is complete or before printing