The white kit with the red and blue sash and the blue one with the red and white sash were both first used in 1972/3. I think the white one came first, because we presumably wore it in the 1972 Charity Shield away to Aston Villa. We used the blue one with the red and white sash as a third kit, but against teams who wore white, mainly, I think (we definitely wore it at Leeds and Spurs). That 1972/3 season was actually the season we wore four kits, because we wore the previous season's red and black away to WBA, where neither of the other away kits was deemed appropriate.
The next season, we reverted to the red and black stripes and stuck with it for 3 seasons, presumably because the two sash kits were Malcolm's design (he pitched up at Crystal Palace and guess who, within a year or two, started playing in all white with a red and blue sash on the shirt). It was in the summer of 1976/7 that we first wore white with a red and black sash. As someone says, there were one or two early performances when we wore it with sky blue shorts and socks before they introduced the black shorts and socks that were specifically designed for the kit.