To be perfectly honest I'm not impressed with this teacher by any means. In the 4 weeks of classes, two classes a week, I've learned more at Youtube U.
Warming filters? Really?? *confused look* Just a thought, but... How about learning to use some of the sophisticated technology our DSLR came with instead? You know, the technology we already paid for and
already have, right there in our hot little hands?
If I found using Auto white-balance was producing snow-scene shots that were a little too blue (due to a bright blue sky reflecting off the snow or, whatever) I would simply try using a different in-camera white-balance preset, such as "Cloudy"; or just bump it manually to 6,500K or so.
Yes, I would expect to need to adjust the
exposure, increasing it a stop or two when shooting a snow-scene, but that's a separate issue from white-balance.