None of our safety folks on Langley AFB said anything about color, I wear a yellow vest and it has never been questioned at all.
I got my hands on one of these backpacks at the IMC in DC this past weekend...the build seemed very sturdy (although I would ditch the arm straps, they seem worthless), it felt like this backpack would be able to take a lot of abuse. I'll pick one of these up eventually, will make it easier when I need to carry something instead of wearing my reflective vest with a messenger bag over it.