However, I feel like you glossed over the proposed workaround, which I feel is appropriate (though more complicated if you want to implement"defade"), and extremely easy to implement.

I took a couple minutes to write an octave script that implement the workaround [1], it would have been even easier if both images had already been distinct files, and perfectly aligned.

The basic idea here is the same as the one behind the YUV transform: our brains are much less sensitive to the chroma channels than the luma channel. So I separate those, and keep the original luma channel, while I use the reconstructed chroma, which is lower-resolution.

Judge the results by yourself, but it seems to me that the end results are a whole lot better: https://imgur.com/a/n2sBYCi

And it could still be improved a lot more (by using the original high-resolution image, and avoiding to hand-align the images).

Edit: also, ironically, the Indigo dye (thus blue clothes) didn't become common before the 1900s [2], so the bias might produce historically-inaccurate images!

[1] https://gist.github.com/MayeulC/626bafbaf925fb3a3c80fdba76b7...

[2] https://en.wikipedia.org/wiki/Indigo_dye#Synthetic_indigo