Here is a 1940's shine.
Not all aircraft were 100% matt, and wind and dirt could polish the surface.
http://i4.photobucket.com/albums/y12...4949u10fg9.jpg
Picture is taken during wartime, see here:
http://forums.ubi.com/eve/forums/a/t...418#6451009418
Look at the sky reflecting in the painted part of the canopy!
The next photo is taken in 1942, as you can see in the link.
http://www.spitfiresite.com/photos/h...-squadron.html
This shows sheen from a certain angle too.
http://www.nasaimages.org/luna/servl...~61&mi=1&trs=3
http://i4.photobucket.com/albums/y12...03-00301-1.jpg
Here too, 1940'sSpits under production. Showing sheen:
http://cache1.asset-cache.net/xc/331...143FD4AE7FC81B
1942, loook at the shine on the tailplane:
http://www.crashsiteorkney.com/useri...tfire164Sq.jpg
A real shiner - Group Captain A.G. Malan, DSO, DFC, with his usual Spitfire Aircraft ZP-A (1940):
http://samilitaryhistory.org/vo013dtc.jpg
I agree that most aircraft looked matt a lot of the time, but depending on different types of paint/wear/lighting conditions they could also show sheen/shine.
.