If this new tail light color becomes street legal you can bet people are going to install it on their cars regardless of autonomous driving capabilities.
(It's true that this will be more difficult to enforce than prohibitions against using darker blue, since a regular passenger car using them is clearly a violation, whereas pulling someone over for the light blue will presumably require the officer to have probable cause that the car is not self-driving.)
Except in the US where indicator lights (turn signals) can be red.
That, or a much more technologically invasive solution like letting cops see into car's driving mode remotely which is a whole other can of worms.
Just like today they automatically bill you for entering in special zones or give you a speed ticket.
They're supposed to add a few speeding cameras next year except ....
https://www.sfmta.com/projects/speed-safety-cameras
See the steps. I suspect it will never actually make it to the final step before some group successfully prevents them from being put up