Whenever I do an animation in AE, I can select any color I please and it changes to that color. Although, when I go to render it, the background is always black.
Does anybody have clues as to why this might be so?
Thankyou hugely in advance! Regards, Scott
Changing background color you are changing only preview window background color. If you wish to make different background color - just make a solid layer with color of your chosing.
The only reason to ever change the background color of a composition is if you are planning to render with an alpha channel pre-multiplied against the new background color. This is a very odd thing to do and only folks expert in compositing would ever need this feature.
After Effects always calculates an alpha channel. If you do not choose to render to a format that supports alpha channels then the "alpha" will always render as black. It is always this way. It always has been and there is no good reason to change it.
As imeilfx said, if you want a solid color you have to add some pixels to the comp in the form of a shape layer or a solid.