Red bands and yellow bands both have a 1:1 high gear and an underdrive low gear; the difference is that the earlier red band used disc-style coaster brakes, whereas the later yellowband used drum-style coaster brakes. A third variant, the blue band, used the drum-style coaster brake, but it had a 1:1 low gear plus an overdrive high gear. The red bands have the strongest braking action; the 1:1/overdrive set-up in the blue bands was imho the best option for gearing, as your low-gear for climbing was the more durable 1:1.
hth