How the heck do I ...
 

In my neighborhood the streetlights read purple to my camcorder (GL1). No problem, just color balance right? There isn't quite enough light to do it -- the the little square box in the viewfinder just keeps blinking and blinking. Is there another way to color balance, maybe on a colored card under tungsten lighting or something? Also, how would I go about matching my lights to the streetlights? There must be some kind of gel that'll do it, but I have no idea how to figure out what it is.

When light is too low, use the Daylight preset WB if you want your scene in warm orange-amber tones. Use the indoor-tungsten preset if you want a more neutral balance.

This won't work for me. I'm shooting outside and all of the presets look really bizarre under the streetlights.

You have reached the limits of the White Balance control on your camera. If you can get closer to the light (stand on a ladder?) it might be bright enough. It is also possible the light source is out of range. The camera white balances within a finite range of color temperatures. Your light source may exceed the range and the camera is warning you of the incomplete WB.

If the color is out of range, do you think it would be possible to use a color filter to compensate? Not that I own a mattebox anyway, but it would be interesting to know. That purple color is really unnatural looking! It looks absolutely terrible.

You may be able to fix the color in post. I recently did a Grad Night where the lights in the gymnasium were really wierd.

The PD150 & DSR-300 could color balance (they were bright, at least) but the PC-110 could not. Some of the exising footage from the school was really bad because their older cameras could not balance the color. I was able to fix it in post.

If you zoom in on one of the streetlights, you might get enough light in your picture to get a white balance according to this light source.
If not, use the Indoor preset if they're amber sodium-type lightbulbs, or the Daylight preset if they're violet-blue mercury-type bulbs. Either way, you'll have slightly wrong colors, but they'll remain constant and easier to fine-tune in post.

It would be easier to white balance on a bunch of warm cards instead of adding filters.

Adding any filter will cut some more light. And you don't have enough already.

Balancing on warm cards was my first thought, but how would I go about figuring out what color cards to use?

I give, guys. Why would you want to balance on Warm cards instead of white cards in this case?

That would be balancing on warm cards inside, where I have control over the light. If I can match the color temperature of the card (under tungston) to the lights outside, couldn't I carry the camera outside and shoot?

Very unlikely you would get good results that way, Marco.

The whole point of white balance is to make the adjustment under the actual lighting for the scene.

A plain white sheet of paper is the best tool for this. Just get out under the lights to do the white balance.

BTW, there is no guarantee that the camera can adjust far enought to give you white in that environment. The street lights sound like they don't radiate across the entire visible spectrum. They probably radiate at a few frequencies instead. If you don't have some red, green, and blue light, the camera will not be able to compensate. Just maybe you could compensate in Post but that could be doubtful too.

Key light?
 

Are you shooting with the street lights as your primary source or do you have a key light for your subjects?

If you do have a keylight, and I am assuming it is Tungsten (3200K) since it seems that you are lensing at night, I would white balance, using the Tungsten 3200 filter, for the key on white and let the background light do its thing.

If you are shooting without a Key, you might want to consider adding at least a small one.

Another option, very time consuming and expensive is to read the color temperatures of the indivual lights using a color temp meter and then gelling them to suit your needs...again...time and money.

Some of these mercury vapor lamps that are found in many arenas and indoor sporting venues react pretty well to a Wratten 20 Magenta filter.

The orange anti-crime sodium lamps are another story alltogether, they are just plain fugly and not very easiy to deal with.

Good luck with your project.
RB