Have been working my way through the Zombicide missions starting with Easy through Medium and now on to Hard.
The nature of the Hard missions means that I can now get my survivors into the orange danger level and also into Red on some of the longer games.
What happens when you reach Red?
Do you continue to track Zombie kills by returning the tracker back to zero and then acquire additional skills as you continue to kill Zombies?
Or is it the case that once at Red you no longer track kills and that is the maximum your character can reach?
It seems to me that at Red it is necessary to continue to acquire additional skills and actions from the second pass over the skills tracker to stand a chance of survival.
I couldn't find any official answer in the rulebook.
With the original rules, once you reached red, that was it. In the Toxic City Mall expansion, they added the optional UltraRed rules that are just like you said, once you reach red, you start back over at blue (still spawning at red level) an gain extra skills once you reach orange and red again. The expansion even included weapons that could only be used once you reached and passed red.
So you could play it either way. All the rule books are on Zombicide.com if you want to read them yourself.
Grab the Toxic Mall expansion rulebook pdf >here<.
There you will find the rules for Ultra Red Mode on page 13.
It's pretty much like you describe.