Disabling the camera auto white balance
Did you check camera properties? On Linux, install 'v4l2ucp', and run it while running your capture app. For at least 'Logitech Quickcam Pro for Notebooks', this shows the 'white balance' setting, with an 'auto' checkbox. We set it to 4000 for our outdoor camera to get true color reproduction. Once you test the camera with 'v4l2ucp', you can script it with 'v4l2-ctl'.

I know many Logitech and Microsoft webcams have the manual white balance setting; I have no idea about other models.

Also, most cameras use two-wire bus to control camera; this includes initial setup (resolution, data format, etc...) and white balance setting. So it is highly unlikely there is any wire you can cut to get fixed WB.