To be fair, a lot of the "gaudy primary colours" reconstructions are based on traces of surviving paint, all of which would have been from the base coat. There would presumably have been more layers of paint on top of that. For a better idea of what could have been achieved if they put even 5% as much effort into colouring their statues as they did into carving them (and why wouldn't they?), look at any modern minature painter.