If it were me and I wanted to keep things real simple, I'd simply leave a slightly warm skylight filter
on the lens all the time, or better yet, an 81A, and expose at box speed (160, internally metered
with the filter attached). This way the lens is protected, and it's a lot easier to correct for a bit
too much amber if needed than for excess blue (which is almost certainly going to be the case at
higher elevations). In the old days, folks would rate the ASA way down, and this would at least give
sufficient exposure to the yellow dye layer, but at the expense of unecessarily cross-contaminating
the dye layer lower down the curve. Portra will give better color purity at rated speed, and it's so
much easier just to correctly filter in the first place. At least, when I'm personally out snapshooting
with a Nikon and don't want to fuss with a bunch of different filters, I just leave the 81A on the
whole time whenever bluish lighting conditions are a risk. With tripod work and bigger cameras, I'm
a lot more specific in procedure.