I would definitely shoot RAW in this situation if the final product were critical. Then you have the ability to view the image on a calibrated monitor and do precise WB tweaking with Capture, or just use some image editing software's levels and curves to remove the cast.
But, it is nice to purchase at least a small grey card that you can always carry with you in your camera bag. Then you know you'll be getting the best measure for the lighting straight from the camera. It is less critical with RAW, but can save post production time. There was a discussion about durable plastic ones that are nice for this sort of usage.