I think you are over-analyzing the photos. They are likely just hand-carving a bunch of boxwood pieces, and then applying different stains for the dark sides. The variation you are seeing is probably the sample variation, not specific to the stain. I also think the pic scaling may not be 100% the same piece to piece. Notice the base diameters also differ with the height.
Zagreb ’59 gilded color options + inconsistencies

HoS has nice shapes/proportions, but I’m not a huge fan of ‘gilded’ (stained or ebonized) when natural wood options are available. The Chess Empire offers the dark pieces in Rosewood and Padauk. The Paduak is too expensive for my tastes for this design, but the Rosewood is quite nice. Some shops make the snouts on the knights too short - they look more like dogs than horses. And some make the necks too skinny.
Staunton Castle has the nicest design to my eye, but like HoS, no natural wood option.
The Leningrad design is similar and gives you natural wood options, but the appeal of the abstract geometry is lost - and the bangs on the knights is unattractive, to me at least.
The Chess Empire padauk pieces look nice in their photos! However, in the photos you showed, the neck of the boxwood knight looks quite awkward, and in both pieces the manes vary in length along the neck. I think the House of Staunton and Staunton Castle ones look much better. Actually, now that you mention it, the Staunton Castle knights seem to have a smaller ridge at the top of the base, which I think looks nicer than the House of Staunton knights. But yeah, a pity that they don’t offer different wood types.
House of Staunton does offer an ebonized and golden rosewood version in their Zagreb Elite (on clearance right now), but I don’t really care for those colors.
And they offer an ebonized and blood rosewood (padauk) in their Zagreb Prestige, which does look beautiful. But $499 is more than I’m willing to spend on this set.

I think you are over-analyzing the photos. They are likely just hand-carving a bunch of boxwood pieces, and then applying different stains for the dark sides. The variation you are seeing is probably the sample variation, not specific to the stain. I also think the pic scaling may not be 100% the same piece to piece. Notice the base diameters also differ with the height.
Yeah I imagine there is some variability, but I don’t imagine there is variability in the heights, so that does leave me wondering which of the bishop heights is most representative.
As for the knight designs, upon closer inspection it looks like they used the exact same image for the Red, Red Mahogany, and Purpleheart sets; all three feature a scuff mark or whatever it is on the right side right above the base. And the knights in the Red Mahogany and Rosewood ones also seems to be the same image. This much variability strikes me as wild though. I wouldn’t want to risk receiving a set with such low-browed knights.
Hi. I’m considering getting a Zagreb ’59 gilded set by House of Staunton, but I’m not sure which color option to go for. It’s predominantly between Red Mahogany and Purpleheart for me; but photos of the Rosewood option seem to be missing on the House of Staunton website, so I don’t know what they look like on the board.
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Colors
Does anyone know how these three color options compare? Which do you prefer? Here are the three options together (Red Mahogany, Purpleheart, Rosewood):
In the pictures above, I like the Red Mahogany and Rosewood options the most; but in the photos on the House of Staunton website, I’m leaning heavily towards Purpleheart.
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King finials
Also, does anyone know what the quality and consistency of the Russian king finials is like? I noticed that the finial of the Red Mahogany option (left) below looks the sharpest, and it’s aligned properly to the crown of the king. The finial of the Red option looks the most blunt, and the finial of the Purpleheart option (right) is aligned the worst. Can they go in deeper, or do these finials sometimes float above the crown? I assume if they float, I can sand down the rod of the finial a bit so that it can go in deeper.
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Knights
Thirdly, which knight design does the set actually come with? As you can see below, the knights of the Red, Red Mahogany, and Purpleheart options have a lower brow, a shorter snout, and squared ears.
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Proportions
Lastly, which of the sets show the correct relative proportions? When I created the images to show off each set with alternating colors with the rook and pawn on the right side, I scaled the whole set relative to the queen to ensure the pieces were shown at the same size in each image. But when I did that, I noticed that the bishop was larger in the Mahogany and Rosewood options. I rather like the proportions of the other options more. Below I superimposed all color options, and you can see that the king, the bishop, and the pawn vary in size relative to the other pieces.
Below, you can see how the Rosewood (left) and Red Mahogany (right) bishops compare.
I realize these questions are probably best addressed to House of Staunton, which I will do. Part of the reason I’m asking my questions here first is to present the inconsistencies and possibly have my questions answered publicly, so that others who are considering buying the set may be better informed about what they will get.