Thank you again for the feedback, gentlemen. I understand the gray card use in exposure settings, but the idea of using a gray card for white balance still doesn't make sense to me. Why would a gray color "balance" (substitute) for pure white - aren't the RGB values different for these two colors, thus causing the DSLR's (my D100) interpretation of other colors to be off since the basis, the "white balance", is off? If any "neutral object large enough to fill the frame will work", why not use a yellow or pink card to white balance? I'm sorry if I seem to be "missing it", I just don't understand. Thanks for your help.
By the way, I did purchase the plastic gray card mentioned above about a week ago, and it is quite superior to the cardboard ones I've seen recently.