If you can find the color photo of Richard Datin & Co delivering the ol' girl to the studio - the one where they're standing on the sidewalk and the ship is in a cradle - you can see that the neck is metallic blue.
I scanned this pic from the April 2005 issue of the STAR TREK COMMUNICATOR, which makes no mention of the blue tint on the neck. And I have not altered the photo in any way:
It's hard to tell from that photo because it's not of the best quality.
I have many internegatives of the large model on the sound stage and the blue on the neck is quite evident (and no, it's not a reflection of the blue screen). If you have US issue #35, 2011, of the Star Trek Magazine (UK #162), you can see the blue in a couple of pictures I restored for the "Lost and Found" column.