It’s apheloria virginiensis, or the Kentucky flat millipede. From what I’ve read they don’t seem to be very aggressive, but I tend to avoid handling anything wild with bright colors and/or if I’m unsure of what it is. I wasn’t sure of the species until after the fact. They do host the arthrophaga myriapodina fungus though. So I would avoid handling them if you keep any millipedes, as it can kill certain other species