Yeah, I was surprised by that too, but if you run the Mini vMac emulator on OSX, Photoshop runs in B&W using halftone patterns to represent colors. Maybe it made sense if the output was destined for the low-DPI monochrome printers in those old Macintosh brochures.

Also, there were some color Macs in 1990, but System 6 still had the B&W UI (screenshot).

To be clear, this was done for the official Photoshop anniversary event, and demoed by Russell Brown at that show. The number of copies we gave out afterwards was limited by Apple's ad-hoc install process for iPhone dev accounts. A wider release would obviously involve some lawyers signing off on things, not to mention all the interface style guide violations in putting 1990 Mac UI on iPhone (I have no idea how App Store reviewers would react to that!)

Yeah, I knew I wrote that part a little too quickly! More specifically, Verizon was recommending that figure on circa-2008 guidelines aimed at their earliest iPhone-style touchscreen phone, which had a DPI that was more or less the same as iPhone, so it's a reasonable rough-and-ready number to cite. (I was at Adobe working on FlashCast, aka "Verizon Dashboard", at the time, so I randomly happen to remember that guideline.) The iPhone HIG is obviously a better reference, but in this app it's sort of moot anyway because the real limit was "as much touch area as we can squeeze out of 20-year-old WIMP GUI". If I can figure out how to boil all this into a few words, I'll clarify the article.