There is no circumstance you can go into that will make DV footage look worse, than to shoot strong red or strong blue. That's a worst-case scenario.
Here's what happens when you have pure primary colors in a DV codec:
Green looks a little better, but obviously pure red and pure blue just turn out incredibly low-res. Avoid pure-red or pure-blue as much as you possibly can. If they insist on doing it, just be aware that you're asking the camera to handle what is, for it, a worst-case scenario. You can try adjusting the color phase some, or dropping the chroma level down, maybe those will help a little, but basically, you're up against it.
I've shot many such live events and it sucks if you can't have preproduction time with the people that work the lights. Sometimes they will work with you and pull out some gels, or use different lights, or adjust them off the main characters, if you ask nicely.
It helps to address them as professionals. Like saying, "excuse me, I could really use your proffesional help". Then explain the problem and ask them if there's anything they can do with the house lights to make you situation better, and of course offer to help or put them back the way they were afterwards.
I also always mention to whoever I'm doing the video gig for that it may suck if we can't have preproduction meeting to address the aforementioned.
Thanks for your reply, I've been away for awhile so have not been able to respond
So is dropping the chroma and color phase all I can do. Is it best to drop it all the way?
I shoot at professional gigs with big labels and stage production and there is no chance of asking the lighting techs to change their show for stage cutaways of performers / musicians,