What I mean is this. Most of the time, I'll have a color key in the background (i.e., 0, 255, 255 ) but when I draw something over it, for example, I write text over the color key on a new layer (using photoshop) the edges around the text or whatever I might draw gets changed to a slightly different color. This is bad because images look funny because what was supposed to be color keyed out, isn't. How can I prevent this from happening?

In Photoshop it's tricky, because Photoshop likes to be helpful and anti-alias everything. Anti-aliasing and color-keys dont mix.
When drawing text there's a check-box to turn it off, which will fix that specific case...

In general though, you have to work in indexed-color mode, so that it is unable to choose any colors that aren't already in your palette (and hopefully your palette doesn't already contain any colors that are quite similar to the color-key'ed color).

Ooohhh, thanks Hodgman! Turning off antialiasing works nicely. There is something else I've wondered but haven't tried yet. Instead of color-keying, if you make a transparent background for an image, will it show up as a white background when you try to blit it to the screen?

That's entirely dependent on how you are loading and displaying your images.