Ro68B -- Or So I Thought

Hi All,
I'm attaching a photo of an RO68b (WD Curtis Match stamp). Scott describes it as green, in the a, b or c paper. This is clearly silk paper type (b), but there is no indication of this stamp printed in blue or any color variation.

I have looked at it from the possibility of being sun changed, but the dark color of the blue matches that of other match and medicine examples, and there is 0 sign of changeling. I find it interesting also that the perf tips on left have part image from the adjacent copy, and they are a match as well.

Anyone have any idea about a blue RO68b?

It's a green color changeling. Some added element, either light or a chemical came in contact with this stamp and affected the yellow aspect of the pigment. Possibly some chemical from the matches themselves, since I have seen a few similar examples in the past.

the phosphorus used in the manufacturing process would also affect color changes. this stamp was previously the property of the cannon match co and issued on pink paper. the pink paper is fugitive and sometimes affects the color of the stamp. both were printed in a blue green shade, some yellower than others. I also have seen this color before and consider it a changeling.

I've seen other changelings, but always with some variation. This seems so completely even. And doesn't impact the paper. Usually when I see changelings the paper is altered as well.
I can accept if that is the only option, but it really doesn't seem to be the case with this one. The blue is a near match (no pun intended) to the RO66b

Not familiar with this. But just im my observation of looking at this on my tablet; I see what appears to be what appears to be a very slight yellowih green hugh, in the central area of the sun and sky.

Curtis came on old paper and silk paper. This appears to be silk. But the color is artificial, a changeling.

Ok, I'm convinced.
Just an amazing even application, which I've not seen before.
But seems to be the only explanation.

They are usually even, when the color goes it usually goes everywhere.

This is definitely a changeling. It would be interesting to see if there is an owners handstamp on the back. J.N.T. Levick, an early revenue stamp collector, made a lot of different chemical color changelings. He was also proud of his work and put his name on the back of many of the stamps that he owned.

I would be more interested if the stamp was on experimental silk paper, would like to see the back. Can you imagine a changeling on experimental silk, what an oddball that would be. (Note: small fiber lower left corner).

Here's a couple more color changling to blue:

My changlings. No markings on back.