Thanks. That helps.
I wasn't sure of the color as I had only seen it briefly until now, but now I can re-create the orange subtitle above. I probably did not see a yellow subtitle.
Further investigation, now knowing the root cause and replicating through causing a DHCP fault, shows that the reason I only saw it flicker is:
1. I disrupt the DHCP for one network which my Hotspot helper claimed. The subtitle is Orange
2. I change the network to another which my Hostpot Helper has also claimed and the subtitle is also orange for a short while until iOS decides the network is fine, at which point it turns to black.
What probably happened in previous tests is I connected to one claimed network which had a DHCP issue but did not notice. Then moved out of range and changed to cellular. Then when I was watching it authenticate to another claimed network, I saw the orange flicker. Not a serious point but did raise a question of why.
Related though, if the network which has a DHCP problem is claimed then the WiFi settings page shows the orange subtitle indicating my app is responsible for it but it remains in an unconnected state - the check mark to the left of the SSID is there but no Wi-Fi symbol in status bar. There is a Wi-Fi with exclamation by the SSID in settings though.
The Hostpot Helper does not get a command so cannot do anything to fail the network or advise the user of an issue. I guess it is confusing to the user to see something managed by an app but not working. It would have been good to get a command informing of the broken DHCP and give the option for the helper to advise the user?