I see no in-game menu settings for it and I looked in the Fallout4Prefs.ini, but all I see there are settings that I think change the color of VATS menu while in PA.
Is it possible to alter the just-walking-around, non-VATS, PA interface color?
God that would be nice. I admit that color grates on me after awhile. Thinking of trying for a purple. Just to change it up.
It's doable. I'm not at my computer right now so I can't be 100% certain how. And, to be honest, I used ConfigTools to set it up weeks ago.
I think it's iPAHUDColorR - iPAHUDColorG - iPAHUDColorB under [interface] ? Or fPAEffectColorR/G/B under [pipboy] ? Might be wrong here.
I also read some times ago that if you go change the hud color while in power armor, it'll change the P.A color, but again, I've never bothered to verify if it's true.
edit: Just realized the "just-walking-around, non-VATS, PA interface color" might refer to the Meters and whole P.A.HUD @ the bottom. I don't think it's changeable without a mod (there are many recoloring the P.A Hud already). But it's definitely possible to change the P.A highlight color.
You can change a lot of things using this http://www.nexusmods.com/fallout4/mods/102/? someone made (for PC). I use mine to fix texture pop-in, made it 10x distance (with zero effect on my fps), now the game looks great all the time.