They are just buses.
I guess the British government just assume that school children are smart enough to get on the right bus without them being individually distinct.
I knew school buses are yellow but I did not realize that they are always yellow. I did not realize that the yellow color meant school. I just assumed that the yellow color was a color busses could be.
Well here in, not the United States of America land, we just have busses. I was not aware that busses required a special magic paint job.
I suppose the paint job prevents school shooters wasting their time.