I came across the Letus Color Temp & ND Fader while searching for good ND Filters. I know all the disadvantages you get from variable ND's (reducing reflections on skin and so on) but the Letus 138mm round Filter got my attention. Besides being a regular ND Fader Filter you can use it as a color Temp Filter. You go from warm to cool...So instead of using the f35 internal whitebalance you could use the setting the camera is strong with and use the filter to calibrate your color temperature. I attached a link for everyone who's also interested in this. There is also a video link with some test shots where he dials in the colors. I just ordered one and will let you know how it performs. Anyone having experience with it?
http://www.ryanewalters.com/Blog/blog.php?id=4421947698389788970
http://www.ryanewalters.com/Blog/blog.php?id=4421947698389788970