I'm still looking for the yellow bordered Reconstruction, and I've found another old WotC employee who remembers these colored border test prints.
I asked his permission to post what he told me about them.
Victor Wertz, editing, typesetting, WotC's Carta Mundi Liaison, jobs to numerous to mention.
Victor was one of the people who helped select the cardstock used for Magic. As liaison, he was for WotC what Luc Mertens was for Carta Mundi. They would have worked together, communicating each companies needs and desires. As such, Victor was definitely involved with test prints made by Carta Mundi.
Vic Wertz wrote:
I know the cards very well. These weren’t made locally by Dave though,—they were actually printed at Carta Mundi.
After printing black-bordered cards and white-bordered cards, we were looking at the possibility of printing cards with other border colors, and it turns out that due to technical constraints at the time—a bizarre limitation related to the maximum size of film recorder output in the early days of digital prepress—Carta Mundi could only offer us cyan, magenta, yellow, black, red, green, dark blue, or white borders.
Since you seem interested, I’ll go ahead and explain further. Carta Mundi’s standard press sheets contained 121 cards, in 11 rows of 11 cards each. Back in the day, we had to provide them film output of our digital files, and there weren’t any service bureaus in the area that could output film of that size. So we used to divide the sheets into four quadrants that were output separately (upper left 5x5, upper right 6x5, lower left 5x6, lower right 6x6), and Carta Mundi’s prepress department would put them together in Belgium.
As you mention, the whole image area is made up of halftone dots. So when Carta Mundi put the edges of two quadrants together, the dots probably wouldn’t line up perfectly; if they overlapped where they weren't supposed to, the overlapping area would be too dark, and if they left a gap where they weren’t supposed to, that would be an unwanted light area. This would translate to a black or white line where the quadrants joined up, and if they took that to print, and if the cards then weren’t cut perfectly on the line, that line could be visible on the edge of the card. But if the borders were monochrome black, overlap wasn’t a problem, and if the borders were monochrome white, gaps weren’t a problem. Monochrome white borders were easy because there were no dots to overlap and gaps didn't show. Monochrome black borders needed tape to cover the gaps.
Now, think about how 4-color printing works, where (for example) the yellow plate is really a monochrome image—where it’s fully opaque, it results in full yellow; where it’s fully transparent, it results in nothing printed in yellow (and if all the other plates are clear at the same spot, it’s the color of the paper, meaning white). So as long as the borders were either 100% or 0% on every plate, then Carta Mundi would have the matching tape to cover the gaps. Which meant CM could do borders for us in only the following colors:
Cyan (C: 100%, M: 0%, Y: 0%, K: 0%)
Magenta (C: 0%, M: 100%, Y: 0%, K: 0%)
Yellow (C: 0%, M: 0%, Y: 100%, K: 0%)
Black (C: 0%, M: 0%, Y: 0%, K: 100%)
Red (C: 0%, M: 100%, Y: 100%, K: 0%)
Green (C: 100%, M: 0%, Y: 100%, K: 0%)
Dark Blue (C: 100%, M: 100%, Y: 0%, K: 0%)
White (C: 0%, M: 0%, Y: 0%, K: 0%)
(Theoretically, there are other versions of black that could be done—for example, C: 100%, M: 100%, Y: 100%, K: 0% and C: 100%, M: 100%, Y: 100%, K: 100%—but printing presses have a maximum allowable ink density, and both of those are likely to be over inked.)
I know we got our own film recorder at some point; I can’t recall whether it output full sheets, which meant this problem ended then, or whether it continued to be an issue until Carta Mundi finally got the point where we began sending digital files instead of films and they did their own direct-to-plate printing. Tom W. would probably remember that better than I. I asked Carta Mundi to print samples of all of those so we could look at them. Turns out they were all hideous apart from black and white, so we never did anything with them.
We received one 36-card sheet (which they had cut into two halves, for reasons unclear), plus a single cut copy of each card on the sheet. The photo you sent shows the top half of the sheet with rows of yellow, red, and magenta; the other half had rows of cyan, green, and blue. So when it comes to individual cut cards, there are 6 cards with each border color, and each card is completely unique.
I’m pretty certain that the cards were kept in groups of 6 (CMYRGB). The Wizards’ production department kept some, and I believe that the R&D department took some, but I’m a little hazy on that last fact. Tom was almost certainly the person I’d have given the cards to for the production archive. (Whether he’d *remember* them or not, I can’t say. Since we had pretty much immediately decided never to do anything with them, they weren’t that big a deal.)