The red colour is the dope on the fabric Jeff, which was on all the interior fabric, except those areas painted matt black, in the cockpit and nose section. The geodetic structure was 'silver', which as far as I know was done with 'Aluminium', a 'paint' made from clear dope and aluminium powder.
It's probable that at least some areas of the frames had a zinc chromate coating beneath the 'silver', as this is visible on parts of the Cosford example.
I'll e-mail the book to you, along with some more pics of the RAF Museum aircraft interior, scanned from the member's magazine, 'Radar'.
Here's a couple more shots, showing the faded red dope, and traces of the zinc chromate on the 'silver' frames, plus a rather poor shot of one of the bomb bay cells.