Google has failed me (or I, it) in locating said books. (My search was: “High school English textbooks, 1970s, hardback, red, yellow, green”) These English textbooks were rather small (maybe four inches by six, but a couple inches thick), hardbacks, and came in a different color for each grade (9-12). Three colors I remember were yellow, red and green. The other may have been blue; it may not have been. I can’t remember.
Anyone from that era remember?
Sir Rhosis
No, they were solid bright colors with the title and editor on front, iirc. Thanks, anyway.
Sir Rhosis
Maybe these? Looks like there’s a different color for every level and the cover designs have changed some over time. Size is 6 by 8 inches.
https://www.textbooknbeyond.com/index.php?main_page=product_info&products_id=1136
Sorry, no. No designs on the books. Solid bright colors with text.
Thanks all for trying.
Sir Rhosis
A long shot, since it doesn’t really match your description, but maybe your memory is fuzzy or there were enough different editions that it’s worth a shot: