So I followed, setting mine as follows
However, the rendered background is still black instead of white, as below.
What might've gone wrong here? Many thanks in advance.
Hold down Shift and press Z
This switches to Rendered Viewport shading and Shift+Z is the hotkey that toggles it on and off.
If this does not work, try uploading the .blend file?
In shading section of the render tab in the Properties panel, change the Alpha from Transparent to Sky (little camera icon). I faced the same problem in Blender render.
Change to the cycles render, I'm using blender 2.79b. Only changing the render works for me.