I have a Canon HFG10 I use somewhat casually and I'm thinking of upping my a game little by manually setting white balance for my shots. On reading up on the process it seems that some people feel it's better to use a gray card instead of a white card. Without going off on THAT tangent, I'm wondering how you'd use a gray card for setting white balance with the HFG10. I know how to set it with a white card. Thanks.