I colored my hair medium auburn, and liked it even thought it faded considerably. But I decided Id like to go back to my natural color (light brown), or one close. I used blonde on it and well, its still red, just brighter and not much lighter. Is red uncoverable?

You really can't lighten hair once you've dyed it darker.  Your best bet would be to dye it a brown color over the red.  Be forewarned though, this is going to put your hair through a lot of stress, especially since you've already used peroxide on it twice (I assume you are using permanent color).  You'll want to do lots of deep conditioning for the foreseeable future.

The ideal thing to do would be to go to a salon that specializes in long hair (or at least has a stylist who does) and have them reverse streak it back to your natural brown.  This would eliminate that all over one-color look you get from dying and allow less of your hair to suffer the ravages of the chemicals.  Though some of your hair will remain red, it will look fairly natural growing out.