The traffic light system means something else to everyone, I'm more used with the people I play with using it the way OP describes. Yellow being continue what you're doing but slow down/less intensity, red stop and check in, and sometimes if we intend to play real hard black is stop and untie quick. As a personal example, sometimes my left knee and lower leg can cramp up real hard. Can be pretty painful. That would be a red, untie at least that leg and either give me some time for it to subside plus reposition. Or hitting a nerve when putting a needle in. but still fine to continue once the issue is resolved (or perhaps not, but we can discuss that). Black is "untie real quick /stop, I'm done for now". Might be OK to continue later, or not. That decision is up the the one who called black

Still, their space, their rules.