Should I use a gray or white card for my G15 custom white balance?

I bought these little cards on ebay. Black. White. Gray. Should I use the white or gray card for custom white balance? What are the advantages of one color card over the other? I take photographs at buildings, and construction sites, and industrial environments where there is mixed lighting. Do you have any advice for me?

When I shoot RAW, I am surprised that changing white balance is still available. I have Lr and Ps. Should I use custom white balance when shooting RAW or take pictures of the white card with the scene lighting to then use in Lr?

Thank you.

Use a grey card. Surprisingly, white balance can be affected by your exposure (and vice versa); if you shoot a grey card, your exposure will be close to correct. If you shoot a white card and let the camera set the exposure it'll be underexposed (and getting a WB from it may be problematic); if you expose it correctly, your file may clip one of the colour channels and you'll get a bad white balance.

^^^ What he said. White will work if you dont blow it out (overexpose).

Timza wrote in post #17918462
....I have Lr and Ps. Should I use custom white balance when shooting RAW or take pictures of the white card with the scene lighting to then use in Lr?....

Why mess about setting custom WB when shooting RAW? If you shoot RAW with AWB set, you can easily adjust if needed in LR. That's what I do.

teekay wrote in post #17919137
Why mess about setting custom WB when shooting RAW? If you shoot RAW with AWB set, you can easily adjust if needed in LR. That's what I do.

Because the closer you are in camera the quicker you can do post. Also the preview .jpg thats the basis for your histogram will be more accurate if you have an accurate wb. There are times when auto wb is fine, there are other circumstances when its terrible.

Some cautions...

1. do not ASSUME that a 'grey' card is 18% midtone, some cards are designed for WHITE BALANCE but they result in not getting a 'proper' exposure.
   
2. do not ASSUME that a grey or white card are truly neutral from the standpoint of R=G=B (neutral) color balance
   

Ok. The cards I bought on ebay are also for sale on Amazon. They are the DGK Color Tools Optek Premium Reference White Balance Card Set. They come with a gray strap. One of the cards is is gray. They say they are calibrated. They have 139 reviews. Some reviews are bad. Some reviews are good. Early yesterday morning I put the gray card on the strap around my neck and went down the street to the church where I vote. There is a walkway where in one place there is a sodium light, and then in another there is a mercury light. I took the below two images. Canon G15. RAW. Sirui monopod. Giottos MH1304 ball head. SanDisk Ultra SD card. Canon battery. I just exported them from Lr with no modifications. Before taking each image I used the gray card to define the in camera custom white balance. The crazy thing is the first scene that turned out more white/cool was the scene that was under the sodium light. And the second scene that turned out more yellow/warm was the scene that was under the mercury light. Crazy. Flip. Flop. Before doing this I was so excited because I was expecting that the bricks would look exactly the same in both images. Now I am so disillusioned!

In general, when taking photographs, I am walking through a construction or industrial site. I am not "doing photography". I don't have an assistant. I don't setup in one place. I can't plan on putting a gray card in the scene even if I had the perfect card. I like the idea of having a card around my neck. Maybe what I need to do is hold the card out to set my in camera custom white balance and then hold the card out at an arms length to actually take a picture of the card. So then in Lr I can select the image with the card along with the subsequent images and eyedropper the card to adjust the white balance of the group of images.

Sodium amd mercury lights are not full spectrum light sources so its impossible to get an accurate white balance. You cant balance colors that arent there in the light. You can shift the colors around to make the colors seem somewhat natural but if the light source doesnt hace enough red you cant get a true balance. Try using your card on full spectrum light sources (not vapor or fluorescent).

gonzogolf wrote in post #17920333
Sodium amd mercury lights are not full spectrum light sources so its impossible to get an accurate white balance. You cant balance colors that arent there in the light. You can shift the colors around to make the colors seem somewhat natural but if the light source doesnt hace enough red you cant get a true balance. Try using your card on full spectrum light sources (not vapor or fluorescent).

To reinforce the point: "Sodium amd mercury lights are not full spectrum light sources so its impossible to get an accurate white balance. "

Many modern fluorescent CFL bulbs (but not all) can be quite good for overall balance when corrected with WB shift and Tint shift. I routinely shoot things after darl for posting on POTN or other forums under home CFL illumination, and it corrects quite nicely...NOT true of sodium vapor or mercury lights however!

Shot under CFL and corrected