With the very poor failure last night, I tried various combinations to make sure that I won't mess it up again, so the first thing to do is to find out what's the correct setting:-
Device set to Y800, Codec set as unspecified.
The above combination will work whether Debayer is enabled or not in IC Capture, if it's enabled, the output file will be bigger but Registax won't need to Debayer it as it's already in color; and if it's disabled, the output file will be smaller, but it will need Registax to Debayer it later. For slower machines, I think it's nice to let Registax do the job later to maximize the frame rate. Y800 will allow 60 fps, and Y800 is also the correct setting for my DMK 31AF03, so I think I will keep using it.
Now, the incorrect setting. I tried to reproduce the incorrect setting last night, to really understand what was going wrong, and I believe I found it:-
Device set to Y800, Codec as Y800.
The above will work if you DON'T choose Debayer in IC Capture, but if it's ENABLED, you will see color in real time, but only b/w is recorded in the AVI, and Registax will not be able to Debayer it afterward.
The rule is very simple. Unless you choose a file format which can support color information like RGB24, don't choose Debayer or else color information will be constructed, but be thrown away immediately if the file format cannot support.
To make even more simple is that, don't choose Debayer in IC Capture at all during recording, it saves disk space, allow higher fps, and it won't lead to any data lost.