Depending on where you live in the US, you can count on strong feelings as to whether the POW/MIA flag should be marched in a color guard for a parade.
The only information that I have been able to find, of which Mike Kelley (DrillMaster002) reminded me, comes from AFI 34-1201, Protocol, :
2.11.10. The POW/MIA flag will always be the last flag in any display.
2.11.11. The POW/MIA flag will always be the last flag in any display, except on the six national observances for which Congress has ordered display of the POW/MIA flag. On these days it is flown immediately below or adjacent to the United States flag as second in order of precedence (however it still would be flown after other national flags). The six national observances are National POW/MIA Recognition Day (third Friday of September), Armed Forces Day, Memorial Day, Flag Day, Independence Day and Veterans Day.
22.214.171.124. The POW/MIA flag is not carried or displayed in parades or reviews, however is authorized to be carried at official military funerals.
The other services do not specifically refer to the flag for a color guard, which can be taken just like bayonets, swords, and sabers- not authorized (the MCO does specifically band bayonets, however).
I know, this is information from the USAF for Airmen and no one else must follow it. The other services do not have information and nothing else exists as far as guidance for veteran organizations, first responders, and citizens. However, military color guards do not (are not supposed to) carry it except during funerals for former POWs and that’s it. Color guards should not carry the POW/MIA flag inside or outside the formation.