I am thinking of the ADDS Consul 980, from 1974:
The display was black on white.
It did support lowercase. Solomon Slow is correct. The Data General C/150 certainly supported "console characteristics" which could disable lowercase transmission (i.e. it would convert lowercase bytes to uppercase before transmitting them to the terminal), and I did know this at the time. But, for whatever reason, I never noticed this machine had lowercase. Why our system operator disabled lowercase, I don't know, but it was disabled as well on our long-serving VT52 which also supported lowercase.
As you can see, bright orange keys. I don't recall the cursor control and numeric keypads, but everything else rings a bell.
Walter Mitty suggests it might be a VT-100. The classroom was filled with mostly Data General Dasher D200 terminals, with three oddballs. One of the oddballs was a VT-52; that one I remember. That's why I know the one I'm seeking was not a VT-100; it would have been too similar. The VT-52, incidentally, was a nice little terminal. I didn't like it at the time because it was too incompatible with DG software, but I could write custom software for it that was pretty cool. (The third oddball was an Apple ][ rigged up as a dumb terminal. That was horrible, and I only used that if everything else was taken.)
However, I'm pretty sure now that it's an ADDS Consul 980, and I thank all of you for contributing.