I have never owned a color printer, and during most of my time as a Netrunner player, I also haven’t owned a black-and-white one (not that it would matter). If I needed a proxy, I printed one somewhere. If I had no time, I did not use the card. I think it is more important to provide my opponents with good gaming experience by using easy to read cards, than to play with a last-minute deck change I cannot properly make.
I have TOd a lot of Netrunner events spanning about 5 years. During all this time, I had a player need an emergency proxy exactly once. Do we really need to solve such rare cases in the rules? Those can easily be solved by a TO ruling when such case happens.