What is "yellow flag"?
A "yellow flag" is a much more meaningful differentiator of "sects" within Lubavitch than any other meaningless label I've seen thrown around here.
For example R' Yoel Kahan (I was going to write that as RY"K, but that could also refer to someone else) believes the Rebbe is alive (to use his own words: "..לא יתיר ולא שמתיר" will post a link when I find it and have a moment), and that he IS moshiach (there's a famous documentary done for Israeli TV regarding "Messianism in Lubavitch" that IIRC starts off with an excerpt from an interview with his Rebbetzin, where she insists that the reporter acknowledges that she is CERTAIN that the Rebbe is Moshiach), yet he does not bear a "yellow flag" and AFAIK might be opposed to it.