Shoot Velvia!

Going back a few years when I used to shoot color transparency all the time we found that Kodak films tended to be blue whilst Fuji tended to be warmer.

It may be counterintuitive but when things got a bit overcast we would always turn to Velvia as it really warmed/punched the colours up - to the extent that we would end up shooting sports on 400mm lenses at 1/60 or 1/125 sec, loads of waste but great colours and no blue faces!

Ooooh, have you thought of a UV filter as that can cut out some of the reflected blue comng from the sky when its overcast. Otherwise 81A, B or C is the way to go or gold colored reflectors.