I have worked for Xerox since the early 80s, and on color products since they came out. From what I understand, Xerox would financially benefit from color products, but the technology could cause chaos with counterfeiting and the U.S. treasury department, which I believe it did anyway. Xerox, a public company, had to include anti-counterfeiting measures to comply with U.S. treasury regulations. The yellow dot pattern only shows the last six digits of a nine digit serial number of the machine that printed it. A binary grid is laid over the dot pattern to show the last six digits. The dot pattern is printed on every square inch of the paper, so you could print your own postage stamps and not get the whole grid on them. You can hard stop the machine while printing and see the dots on the imaging belt or photo drum after you remove from the machine. You can also program the machine to perform a color conversion and convert anything yellow on your original to black and get a copy with a bunch of black dots, that's providing the original is printed/copied from a color machine. You can't change the serial number! The serial number is stored on three different components of the machine. If those three don't sync, your machine don't work.
So if you printed money and someone caught you, then all they could do is call xerox and ask what customer has the serial number with the last six digits of xxx-xxx. Even then the machine could have been resold several times and who tracks that? In 1992 we had a guy print $40,000 in 100s to buy cocaine. The dealer turned him in, not the dots.