White balance help?
 

Shot San Francisco this evening from magic hour to fully dark. Brought a white card to re-set proper white balance as the light changed. Not happening. Once the sun dipped below the horizon I couldn't get the cam to read the card. Cam kept saying "No subject". I kept saying back, "Yeah, there is.. It's right there in front of you..." Nothing doing. Auto WB looked horrible once it got dark and my two presets were both above 5k.

My D200 which lets you set WB manually, incrementally, looked pretty realistic @ 3500k but I couldn't get the JVC there in the dark.

What could I have done (besides known to set one of the presets to 3500 before I got there)?

First piece of advice is to familiarize yourself with the menus, to change the WB preset is no big deal if you know where to look - it only takes a couple of seconds.

If you get the "NG OBJECT" message it's because the color temperature has dipped below that which is recognizable by the camera as there simply isn't enough 'white light' striking your white card. Assuming you still had a proper exposure at that time you could have tried white balancing off another surface. Though, if it was me, I'd have used the 5k preset.

Why WB so frequently, do you need the shots to match? Were you shooting scenery or people?

Unless you're are using a warm card or similar technique, white-balancing at sunset is a sure-fire way to kill all the beautiful orange/pink and yellow hues. Just because is says in most manuals that sunsets are around 2-3k doesn't necessarily mean that a tungsten setting is best particularly as sunset is actually a mixed light situation - you might have 2500k coming from the sun but over 10,000k coming from the sky - it all depends on your shot.

I was actually OK during sunset. It was the night shot where things looked off. Simply city skyline shot at night. Only problem was the lights of the city all looked way too red. White buildings lit with white lights all looked red as well. You are right, 5k during sunset was fine. After that it all went to hell. I've never manually set white balance in the menu. Didn't know we had that option. Thanks, I'll look into that.

Why WB?
 

Personally I would only White Balance once in this situation, or better yet use preset. You don't want the light to look white during sunset, you want to see that the color of the light changes. If you keep white balancing, orange light will look white, not orange.

Maybe it's better that I ask this differently.. Forget the sunset for a moment. Let's say I just wanted to set proper white balance for a city scene at night, but none of my presets were in the proper range, the cam wouldn't read the white card, and auto WB was way off. That was my main problem(s). I still have yet to explore manually setting wb in the menus, but I'm looking forward to it.

When shooting at night or shooting sunrise or sunset, I normally just use either a 3200k preset or 5600k preset, depending on how warm I want the image. I can make minor colour correction in post.

Yeah, that was my goal, to get to 3200. I just couldn't get it there as the only way I knew how to adjust was shooting at a white card (also tried a gray card), or trying auto wb. Neither worked though. Cam said "No subject" aimed at the cards (even though it looked pretty bright in the view finder with 1/6 shutter), and auto made all lights look orange/red.

Move the WB switch to PRESET. You can then toggle 3200K or 5600K in the CAMERA OPERATION menu, or assign one of your user buttons in SWITCH menu as the toggle button.

Thank You!

Just an addition to what's already here. I always keep the preset position for "presets" and one user switch to flip 3200/5600 - but you can change how that switch works. Maybe you set it to be auto white? I find that much less useful.
Manual white card balancing a sunset is definitely a bad idea for the reasons given here, and a common mistake for people starting to assert control over their cameras. Much of what we shoot has mixed light colors in some form, and choosing where to balance can become more of an emotive decision than a pure technical one. Just tipping your white card up or 2 one side can make a dramatically different reading and look.
More to your point, the light on the card you hold in front of the camera is not always the same as the light on (or from) your subject. A dark building with lights may give the most pleasing white balance just by zooming in and balancing on the dark building and lights.

I tend to keep my default Top setting to manual for 95% of what I shoot. KISS Keep It Simple Stupide mode for top, Me/manual white balance with every tape change or every scene change. (which ever is sooner)

The middle setting I keep as a backup set at to 5600k for odd changing outdoor lighting conditions. When all else fails outside, one click down and a decent 5600k balance for adjusting later in post. Most of what I do is outside so this emergency backup method works for me.

AWB? experimneted with and never liked, but could be usefull if doing long uninterrupted takes in changing light conditions. Walking indoors to outdoors a lot.

If I were doing a lot of interiors, (not often) I change the middle setting to 3200k as a backup if I just can't get the white card to the location of reflecting the keylight. For instance a musical performance shot from the rafters with mixed changing lights.