Side by side..
Well, I have gotten around to doing a compare on the decks.
Haven't been able to dig up my copy of the 2nd 1976 version (the one with four languages), so these impressions are just from the 1976 1st edition and the new reprint:
The new print is a wonderful work - It has been a lot of fun looking at the decks side by side.
Cardstock is ever so slightly thicker in the new version: Deck thickness is 1.1 in 1st edition, 1.16 or 1.17 in the new print.
There is a tendency overall for the painted fields (backgrounds and the like) to become more uniform. The original has a lot of visible brushwork and washovers that get considerably smoothed out in the new deck. There seems to be a tendency as well for the color of the overpainting to shift toward the background (III Consort - wash over the sun in background goes from grey to brownish yellow). This all gives the visual impression of the new deck being a bit 'softer' in the fine details.
The colors in the majors lighten, as we see in Sumada's picture of XVIIII Sun above in this thread. This is in both white level and in hue - reds pull to orange, earthtone yellows become more lemony. Skin tones become less brown and more flesh or orange-ish. Pinks and purples become less blue.
But, the lightening is not entirely consistent: An interesting card to look at is XIII (Dead Man): Here there is a strong red background in the upper portion in the original that turns into a mostly orange field, with part of the region staying red. At the same time, the greens on the card get deeper, and lose a yellowish tinge to become more emerald.
Grey blacks become brown in hue, especially the hieroglyphs in the majors. This is the case to a lesser extent in the card titles of the minors.
In contrast to the majors, the background fields in the minors become more saturated. Pale yellow and turquoise gets a lot brighter. The turquoise and yellow backrounds are most modified, the green the least modified.
In the case of the turquoise cards (Cups), the greater background saturation is accompanied by a strong evening of the color. They look less painted, more 'posterized'. This does not mean that all the card backgrounds are the same turquoise. The backgrounds vary a lot from card to card, just as in the original. I think this is a very good thing - the variations between cards are one of the things that makes this deck so dynamic and alive.
Well, although my notes may sound hyper-critical, the new deck is indeed lovely and is very strong work. I think the subtlety of the differences is in fact a testament to the great effort that has gone into producing this new edition of the Xultun Tarot. Kudos to Kahurangi Press for giving so many more tarot people the chance to experience this deck.