As Alan was eluding to in shooting RAW, a RAW file does not have white balance applied until post-processing.
If you do a custom white balance (CWB) using a gray card or an expodisk the white balance information is stored and given to Lightroom (Lr) or Adobe Camera RAW (ACR) for post-processing and can be applied then.
Another option is to take a shot of a gray card or a ColorChecker Passport in the same light and use it to set white balance in Lr or ACR using the little WB eye-dropper tool. A second benefit to the ColorChecker Passport is the ability to create a color profile for your camera's sensor that can be used in Lr or ACR to correct colors for the individual camera sensor. You can then shoot, say, a wedding, with multiple cameras and have all the colors match regardless of the camera used!