Why is one 340 connecting rod bronze color?

dibbons said
The hodgepodge 340 I am working on has one 340 connecting rod casting #2899496 which I guess was used on 68-73 340 which is the normal gray steel colro. The other seven connecting rods are casting #3418645 which I guess are 74-80 360, 76-86 318. Six of those rods are the gray steel color.

There is one of the #3418645 connecting rods that is a bronze color (all the other rods are a gray steel color). Anybody have a guess why the color difference? Thank you.

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View attachment 1714945348
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Notice other differences between the two pictures? Take a look at the sharp edges under the nut on the non copper colored rod. I was told that these were colored by shot blasting and the smoother edges of the copper colored rod would seem to bear that out.....