Thanks Cliff for the reply.
The culprit for the black Mag icon is, when I checked the Mag setting page, the Mag usage became "Aux only", instead of the default "Both", and Mag type became "Flexi", instead of "GPSV9". But I swear I did not change them. Weird.
After I changed the usage back to "Onboard" and type to "GPSV9", the Mag icon turns orange (off by more than 5%).
I then tried different values on the warning level, from the default 0.05 to max of 0.15, I finally settled down at the lowest value of 0.12 to get a steady green Mag icon. Once I get a green Mag icon, the ATTI and STAB all turn green (@INS13).
What is the significance of increasing the warning level to 0.12 from the deafult ? Pls share your opinion.
One last question, during the above learning process, the Config icon in the Health panel suddenly turns red, but it was green before. And I am quite sure I did not even go to the Flight Mode Switch Setting page after the Config icon was green. I just have no clue on what the conflict is on the config. Appreciate your comment.