Yes, he used the red filter to effect. But it certainly works for me in the likes of 'Monolith'. Surely it takes some confidence in one's vision to apply a filter like that to snow and granite, when you a half way up a mountain with 100lbs of gear in winter. (Not like you could nip back the following day because it didn't quite work, or the exposure was a little off).
I believe he also used a wratten yellow a great deal; in 'Aspens' for example.

Seeing an exhibition of twenty or twenty five images would probably have enough. But seeing the fifty images he regarded as his best together in one place, gave an appreciation of the depth his achievements. They had to kick us out after closing time on the Sat!

Happy New Year to you too David!

Regards, John.