[Dan_San_Abbott]

Gentlemen:
I dissagree with Alan's supposition that it was engine exhaust soot. That might explain the color if the fabric sample came off the fuselage and tailplane. Also why isn't on the rudder? You would not have engine exhaust on the upper wing crossfield. The Color of the red on the upper wing fabric in the Imperial War Museum Collection (1972) matched the color of the piece of 425 fabric I had, DARK RED.
But most of all the fabric alongside the crossfields on the fuselage, and upper wing are dull dark red, about Methuen 10F8. I don't think it is soot, I think is is carbon black added to the vermillion to darken the red and was poorly mixed. One eye witness report of the color of MvR's 425 at Bertangle, stated it was maroon, that is hardly bright red. However, that is closer to the fabric samples I have seen. Everyone keeps looking at the bright red crossfield as saying it was bright red. The red oil based paint that was painted over the flat white oil based paint has bled into each other and has lightened the cross field over time. You will not find photograph of a cross field on 425 that is a light grey tone. In all the photos of MvR's Fok.DR.I (either 477 or 425) where the crossfields and the surrounding fabric are the same dark grey tone, don't take my word for it go look for yourself. What is painted red on the 477/425 was all the same tone of grey, not light in the fuselage cross fields and dark every where else.
The whole machine was dark red including the cross fields.
Blue skies,
Dan-San