In favor of bright colors
In many discussion on this and similar forums, advice is to avoid bright colors. “Blend in. Don’t stand out. Be thee grey man (or gal).” This can make sense in situations of civil unrest – riots, etc. but this is only a fraction of the total range of survival situations. In many of these other situations, prominent visibility is critical. A good way to achieve this is through brightly colored gear and clothing.
I have lost track of the many hours I have spent searching for victims wearing faded denim and tan T shirts. If they would have had a red bandanna, it would have been a big help.
With backpacks, the important qualities are proper fitting, capacity, and weight distribution. Color should be a minor consideration. Unless you are literally in a combat situation, bright colors are often useful. Back in the 1950’s, you could only obtain mil surp packs or civvie packs made with dull colors. Doing field work at the time, we resorted to fastening bright ribbons to our packs so we could find them easily enough in thick brush. Bright blue packs were a godsend.
Conditions may change radically, even during the same incident, so the best course is to have a variety of colors available, as well as the usual signaling devices – mirror and flashlight – even a bright red bandanna can be useful, although bigger is better.
One of the most useful clothing items I ever had was a reversible down jacket -dark green on one side and international orange of the other. I wish I had more stuff like that. My current go to pack is a bright red, though I have others less brightly colored. If the mob is after you, they will want the goodies they think are in your pack, regardless of its color or “tactical” webbing.