Yep, that's a NACA duct Matt, which should have a red border around it, with the words 'Fire Access', also in red. I know the markings you mean, which were angle indicators around the thrust nozzles. I've recently obtained a magazine which has some good colour shots, including detail ones, of the new colour scheme and markings. Just shows the state of our Forces over here - reduced to three squadrons of Harriers now, including Royal Navy, under the banner of Joint Harrier Force - or was it Farce!!??