Green days are days where my mental resources, or "spoons", if you've read the Spoon Theory which I've mentioned here before, are consumed at a rate that I can endure. I come home tired, but not spent, exhausted, wasted, and wiped. And yes. All those words apply together.
On days when I have maxed out my mental, physical, and emotional resources, it is an accomplishment I have the energy to walk from work to the car. It is a wonder I can start the car and drive it home, to say nothing of turning the key in the lock to open the door.
If I sit very, very, very still for a little while, enough will come back that I don't fall asleep wherever I stopped, and that'll be enough to unwind with so I can eat, maybe catch up on social media, spend some time with The Spark, before I call it a night, take my meds, and go to sleep. Some nights, I do not get enough back that I remember the meds. Some nights? I don't get enough back to make anything to eat. Some nights, I do not get enough back to do anything other than go directly to bed: do not pass GO, do not earn a damn thing.
Sometimes, I'll just start down from my max, and even a green day will leave me like this.
Stick around. I'll describe yellow next.