Weren't US Lincoln cents made from a more yellow colored metal just after WWII? I recall something about it being the same alloy as used for cartridge cases, I think it is called "cartridge brass".
A small amount of brass from small field guns was added to the bronze normally used to encourage the populace to save copper and give to the government. 1944 is the mintage most mentioned. It was deemed too dangerous to retrieve the copper from the big guns of ships or on the battlefield. But such did cause the citizens to have several copper drives. Chemistry allows us to change the color of cents to goldish or silverish color and chemistry instructors from middle school to college do it to amuse and impress students....who then tend to put them into circulation , thousands of them.... https://www.google.com/url?sa=t&rct...Pennies.aspx&usg=AOvVaw3yzonwLYmDwPhRPaDzaOXA
My photography skills are possibly not as good as yours, but a tip I picked up from here was to adjust the white balance. I usually use a white background, or when cropping in PhotoScape if I used a black background, I simply color a corner white, use that to set the white balance and then crop it out. As far as grading, I find it difficult to separate MS-63, -64, -65 and easier to grade F, VF and EF.