And yet other pictures of famous people in these textbooks were/are in color. There is a visual discrepancy in presentation and it misleads the viewer (children in this case) in a way they may not even realize for years or decades after. Whether this particular discrepancy is purposeful or not it is problematic.
There are color photos out there, ain’t a hard thing to look up. Journalists were probably shooting in color even if they weren’t getting printed that way since the average person could have a color camera by that point in time.