Yes, daylight does get slightly bluer at higher altitude because there’s less atmosphere filtering the sunlight. But altitude itself should not create a magenta cast. A strong magenta/brown tint is more likely caused by the camera’s auto white balance or other processing reacting badly to a very blue scene, rather than by altitude alone.

At high elevations, intense blue light and blue-heavy landscapes can confuse AWB. Some cameras/software compensate by warming the image too much, pushing neutrals and shadows toward magenta/red.

To avoid it next time:

• Don’t rely on Auto White Balance in these conditions.
• Set a fixed daylight/kelvin white balance, or use a custom white balance from a neutral target.
• Keep WB consistent across clips so color doesn’t shift shot to shot.
• If possible, shoot RAW for stills and the least-processed video profile available, which gives more room for correction.

In short: altitude makes light a bit bluer, but your magenta cast is probably an AWB/processing issue, not a direct atmospheric effect.