I have a pinkish cast to my photos that usually occurs on the white portions of the shot?

If I'm using a combination of bounced flash and natural light, what do I set my white balance at? (Using a Nikon D-90)

Added (1). In some cases it is a mixture of natural light and a bounced flash. But in the really drastic one I took yesterday inside a soft box… I just had basic cheap work lights shinning through muslin on all sides. The photo looks great except for a pinkish tint on half of a white plate.

Best to shoot in raw & adjust in post, or use a white card & do a custom white balance.

Are you bouncing off neutral walls? Are there fluorescent lights on anywhere?

You have answered your own question when you say "it is a mixture of natural light and a bounced flash". Mixed light is the most dreaded, most difficult of all things to control. Unless you use a gel on the flash to match the ambient light OR take the photo in either 100% ambient light or 100% flash lighting, you are going to typically have problems. Also, as deep blue said, even if you base all your exposure on the bounced light, if the walls / ceilings have color, then this can also be in your photo. However, as it will not be MIXED lighting, you can use a proper white balance method to overcome any color cast.