[toni-a]

Can you please clarify?

that would be correct if you will shoot one scene and not set a profile for the filter. you shoot the grey card with the filter mounted set balance then shoot, however you can do better and profile your filter.

in fact every camera needs calibration itself and  if you are a color accuracy fanatic every camera/lens/filter combination needs calibration  , You shoot a color target with the  filter and set the color shifts using software you save the profile , this way when using the filter you set the new camera profile and everything is  automatically corrected

here's the hardware and software to do it, it's not expensive but time consuming  

http://xritephoto.com/ph_product_overview.aspx?ID=1257