Here is a gif image with lettering and a transparent background. The colored background comes from the background attribute of the enclosing div.

Here is the same gif image against a different color

These letters were generated WITHOUT anti-aliasing!

The same example is now shown with anti-aliasing AND assuming a white background.

... and again the second background.

Because the second example was created as anti-aliased text blending to a white background there is a disturbing "halo" . As you can tell, blending to a second color, typically white, can lead to text in graphics that looks horrible if later a website's background changes.