If you want a white background you have to put a white solid or a white image on the bottom of your comp. Adobe background color does not change the fact that it's an alpha channel unless there are pixels on it and alpha channels always, let me repeat that, Always render black.
You are not the first newbie to get caught by this.
The only possible reason you would ever change the background color in the composition settings would be if you were going to render an alpha channel with a pre-multiplied color. The standard for all nonlinear editing systems and compositing apps is to treat everything as straight Alpha. And less you know exactly what you're doing and have a custom workflow set up there is no reason to ever change the background color of a comp.
THANKS SO Much!
I am new to After Effects and so this language you are speaking of is new to me.
Am I to assume, that in video we always and only FADE TO BLACK and that is what you mean by "Alpha"?
And just an FYI, the reason why I am looking to have my background white, is because my Power Point slides have an inherent White background so that's where the need for the white background is coming from.
Alpha just means transparency. The background color you set in the composition settings is just for preview purposes so you do not have to look at the grey and white checkerboard pattern that represents transparency. If you do not put a "true" background into your composition (actual pixels) then it's going to render as transparent wherever your composition background was visible. If the file format you render to does not support transparency channel (alpha channel) then it will show up as black.