When I moved out and started doing my own laundry I separated light and dark colours but then gradually I stopped doing it when I realised nothing bad ever happened if I mixed everything together. For most of my life though I've been quite careful about keeping brand new dark items away from white items until they'd been washed a few times. A few months ago I accidentally washed a new red t-shirt in with some white things and they stayed white. And we got some new dark things recently and because of the experience with the red t-shirt I didn't separate anything and still everything is fine. Have dyes modernised or something so that they don't run and you don't actually have to do this anymore?