As near as I can tell most paints are out. 10-20 years max, and any UV exposure reduces that dramatically. A north facing wall can help but in a shore side (not salt) environment in Arizona that isn't as much help as it might be elsewhere.
I looked at powder coat, and the best powders start to fade in 20-25 years from what I have read. That's assuming other factors have not harmed them.
Red metals aren't really "red," and they would need to be coated to prevent corrosion. Brass (gold finish) red metal is already being incorporated in the project.
Red anodized aluminum seemed to be an option, but quick checks (not exhaustive) seemed to indicate that organic pigments used in aluminum anodizing will fade. My cursory checks didn't show an inorganic red for aluminum anodizing.
I am prepared (and the person asking is prepared) to leave out the red for these reasons, but I want to make sure I have exhausted my options. No red rust isn't an option. LOL.
I'd like it to look good for the maximum remaining life span of those asking. Maybe as much as 50 years barring further life extension results in medical research.