With the switch from incandescent bulbs to LED traffic lights it would be very easy to change the shape of the lights: e.g. octagonal for stop, triangular for caution, and circular for go. Keep the colors, but add shape as well. Seems like an obvious and useful change to me.
If they're roughly the same size and in the same order as the round lights today, people with poor visual acuity would still see more or less what they see currently.
