Ideally, you set aperture (iris) and white balance during rehearsal, and leave them that way for the performance. If you don’t have the opportunity to set them in advance that way, you should set the white balance to a default preset for “indoor” (about 3200 degrees Kelvin) and then you’ll have to adjust colors in post production as needed.
Something that will help you in post is to shoot full frame of a white card, just before the show, and use that as a point of comparison when adjusting colors later. Ideally, you’d shoot a color bar chart on location; or what we call a “Macbeth chart” of color chips – that’s a bit more advanced, but really helpful in post for getting colors right. Color bars that are electronically generated in the camera don’t do you any good here: you need to see the colors as they have come thru the lens, under the existing lighting conditions, onto the sensor.
Here’s the thing about shooting theatrical material with a “prosumer” camera. Stage lighting is not “normal” everyday lighting. It’s done not just to light things to be seen, but also for dramatic effects, so if they throw up a lot of red or blue in a scene, that’s intended… but an auto-white, auto-iris camera doesn’t understand that. It’s going to try to un-do the lighting director’s work and “correct” it to make it look like everyday daylight or tungsten. And auto-iris is going to obsess on the brightness level of one , small bright white item in your frame and clamp aperture to that, making everything else around it too dark. Or it will concentrate on a large dark area and over-expose, blowing-out people’s faces. Then what you get looks like junk.
So in these kinds of settings I recommend all-manual settings, and yes, that may mean manually “riding” the iris controls up and down to keep a reasonable level of exposure as you zoom in or out. If your camera has “zebra bars” as a display option in the viewfinder, turn those on and learn how to read them. They will show you where you are in danger of over-exposing.
The most important thing to capture on stage is a clean, well-exposed FACE. Everything else takes second priority to that, because nobody can or will watch blown-out faces. You can bring up the mids and blacks in post, but you can’t restore blown-out detail, so make all your exposure and color decisions while shooting based on making the FACES readable and clear.
This is also another reason why shooting with two or more cameras is so useful: the wide shot and closeup shots can stay fixed at the proper settings for each, without constantly having to ride their iris.