Flat Aluminum - Tamiya AS-12 spray is a great match.
British made tanks used a flat aluminum interior color until just after WWII. Lend lease vehicles were in flat white as per US standards. Black and white photo's will not show much distinction between the two colors.
Modern restored vehicles seem to be painted flat white for the interior whic adds to the confusion.
Mike T.
Edit:
For the Matilda this would be accurate: additional information is that many, but not all vehicles built during the later part of 1942 to the middle of 1944 may have white interiors as a shortage of the aluminum pigments gave the aero industry priority use on it. Matildas used in North Africa should have aluminum interiors while the Mk III's and Mk IV's used in the Pacific may have a mixture of aluminum or white interiors.
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