I think your color guard person handled this very poorly...at least if it were my program. Why did the kids think they would audition on another day?Why wasn't contact made before the audition started? Why didn't the sponsor tell the judges to allow them to audition once they did arrive?
The handbook says membership by audition...does it say the one and only audition time and place set in stone? If this is me, I fight for my kids and I start to wonder about the intentions of the color guard sponsor.
Also, this falls into the work together with other programs and such. If my kids were to miss basketball tryouts because of state marching contest, I would be in that basketball coach's office before we booked a hotel in San Antonio to work out a compromise for my kids, to make sure they don't get put in a bad situation...and my basketball coach would work it out with me because we've built that relationship. Fix this, quickly, and build the relationships back.