Hi, I have a coin book with every Jefferson coin up to about 1976 and they all look 40-63 accept for every war era nickel where they changed the composition to copper, manganese and silver. These have a black tinge to them. See photos:
I suspect the manganese oxidized? I don't really know. I put them in saflips and dunked one into acetone just to see what would happen, but the tinge remains.
That's totally natural. The pictured coin is actually not bad looking at all for a circulated War nickel. The really well worn ones often got quite black (well, dark battleship grey, anyway) in circulation. Laminations and other planchet quality issues plagued the series. The slightly different color of a War nickel always stuck out like a sore thumb to me when I was hunting nickel rolls back in the day. I'd get excited to see it, because once upon a time, I used to be able to pluck quite a few out of circulation.
Manganese doesn't play well with the copper and silver, I'm surprised it doesn't cause more problems on the dollar coins. Possibly because it is a much lower percentage of the alloy.
I have seen a lot laminations on war nickels. Back when I was kid, you could grab them out of circulation. I put together a couple rolls when I was high school and sold them when the silver price made them worth more than their face value. As for the way they tone, yes, most of circulated pieces are unattractive. They look quite nice in Proof and Choice to Gem Uncirculated. I have never seen one with beautiful toning. I have always liked the 1942 Proof War Nickel.
I personally don’t find the (non-crusty) circulated ones unattractive. Just different. They are what they are, to use a cliché.