Color Variety Of 24-Cent Old North Church (1603B)

In case noone has noticed, Scott has added a new color variety to its 2019 U.S. specialized catalogue. This is the 24-cent Old North Church issue from the Americana series, issued in 1975. 1603b only differs from 1603 in the background color ... "greenish blue" rather than "blue". Does anyone have a stamp to act as a candidate for 1603b? Note that the CV for the two varieties are identical, so one might assume that both are common. But Scott does occasionally err in this regard. I do know that there supposedly are color varieties of 1603 in existence, I just don't happen to have any. I can't believe the difference is too great since it took over 40 years for it to be officially noticed. Am curious to see a scan/photo of what others think the stamp might be.
John

John,

This is interesting to me, so I will give it a go. I have 32 copies of this stamp in my used USA stock. I laid them out all out on my desk, and was not sure. Then I flipped them all over, and was able to see differences. See my two scans below. All stamps are flipped over in the same position between the two scans. Not sure which row is blue-green to Scott, but I will guess bottom row? What do you think?

Linus

Here's two mint, NH copies from my collection. Whenever I find a difference in color, I keep it. This was significant enough to warrant the second copy.

Thanks for the photos! While it's a bit difficult to judge minor color variations on a computer monitor, I believe that the "bluish-green" candidates appear lighter in color than the others. I find it especially interesting that the color difference seems more noticeable when viewed from the "gum side" of the stamp.
This at least gives me an idea of perhaps what to look for.
Again, thanks!