I'm working on a novel, trying to write 1000 words and/or 2 hours per day, and I've noticed something surprising. On the days when I write, colors look brighter. On the nights after I write, the sky is a bright, jewel-toned blue, and street lights are surrounded by a misty halo.
I don't mean this figuratively. I mean that the world literally appears different, almost like an acid trip (but much less intense). I've never heard of this as a side-effect of writing.
When I was in my early twenties, I tried to write a novel. I had to stop because it gave me nightmares, horrible nightmares, about killing babies and rivers of blood and injured animals. I was terrified to go to bed. They stopped as soon as I stopped writing. I haven't had anything like that this time, thank goodness. I've had vivid dreams, but only nice ones, and the strange perception with the colors, which I absolutely love.