I wouldn't mind seeing this thread re-vitalized with more contemporary understanding of what the body is doing and what the watch sensors are detecting. I too see considerable amounts of "orange" stress…
I've noticed that mine is more orange when I've had caffeine or alcohol that day or in the previous few days. When I go several days without caffeine or alcohol, it is almost all blue when I sleep. Caffeine…
Relative to workouts during the day, I have definitely observed a range of stress responses at night that correlate with workout intensity. Of course race day efforts and really hard workouts spike and hold my stress high for many hours (day+?) afterward. Additionally, lack of any activity at during a day negatively impacts my sleep, but perhaps not directly or exclusively through stress scoring. A 'Goldilocks' amount of workout intensity definitely improves my night's sleep, but I can't predict a-priori what an ideal workout would be for that day nor know what to do if the training plan calls for a different intensity that day. Casual walks of around 2 miles seem to have benefitted my sleep at least sometimes, but those rarely show up in my training plan. 
