Ahhh, the invisible outlet ......
As far as i know, all the invisible outlet manufacturers have time transported back to the Mother ship and are recharging their light sabers.
Common sense tells me if you build it into the bookcase it will be inconspicuous as long as it isn't chrome plated. You may want to use a GFI which has a small green light which will give it a hi-tech look. Outlets come in grey, white, Almond, brown and metallic. Pick your poison, what ever looks best. The box it fits in will be the most conspicuous, so paint it a color that will blend in.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)