This might be a mystery until someone on set can actually ID the number or we get a really good BTS shot. Here is a comapison shot of some 37s and 38s along with the screen caps from the finale. I adjusted the bright/contrast on the 2nd set just to bring out the details.
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Also here are two different 38s that I own and show how differently they can look just from natural wear and tear unless they came with different finishes when new. The one on the left is much drier and softer than the other one that is still firm and glossy.
I thought the upper parts of the on the screen ones looked more tan than brown. They would be much darker from being soaked so it is hard to say. I don't want to dunk my boots in the sink for an hour to find out but if I come across another cheap pair I might try that
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Screen photos are always hard to use when judging true color. I initially would have thought that the 38 was right because of how they fade. If anyone has a pair of 37s that are worn and can take a clear photo in natural light that might help.
I will play around with the screen caps and my photos to see what I can come up with.
To argue against myself I notice that the finale screen shots look like the threading around the top edge of the boot and the pull tabs looks dark which is how the 37s are.
There was also mention a while back that VM2840 was a match for this pattern too and they have no grain texture on the foot. I think I can see grain on the screen shots here though.