How dark the sky turns with a red filter really depends on just how blue the sky is. Unless you're really high up in clear air, don't expect a
dramatic effect. I was referring to its use to retrieve detail thru haze, since long wavelengths are the least scattered by particulates. Yosemite
Valley isn't all that high, and there is a fair amt of smoke around in the summer. I don't understand why anyone would even want a campfire
down there... but it's sorta a camping custom there to help other campers sneeze all night. Up at Glacier Pt at mid-elevation the air will be
clearer, and up around Tuolumne and Tioga clearer still, provided forest fire smoke has thinned out... you just never know this time of year.
But a summer visit to Yosemite would be incomplete without driving up to the top.