I'm sure cost had a lot to do with making it black and white as opposed to color. But black and white wouldn't have been totally unreasonable in those days. There were probably still a number of people with black and white TVs or who could only afford a black and white monitor. And in office productivity environments, color wasn't always necessary. Case in point, the A2024 monitor, which sacrificed color (and refresh rate) in order to provide a hi-res display for DTP programs.
