...it would clash with the living room decore.

Well then, how 'bout a snow or graphite iMac? I suppose indigo would be a little too much contrast.
The living room is also rather too large for really intimate supervision.

Well then, how 'bout a PowerMac and a nice big cinema display. :-)

Going places and sees things forbidden is a social problem best solved with social means. Risk of embarrasement is very meaningful in that regard. Sitting in the livingroom exposed to view is an excellent reminder. Tandem surfing (parent & child) works well on many levels too.