Or am I just suited by personality to this type of day? Or is there something else?
Some positive reinforcement happened that spiked this visual memory with a good mood? I think it might be that. And if it is that, I think I have to chalk to Ursula K. Le Guin's book A Wizard of Earthsea. I'm pretty sure it was early spring when I read that book, and the notion stuck in my head that the protagonist's home enjoyed a northern maritime climate. So, there was the evocation of that world, but also the characters who were, mostly likeable, but mainly real. Maybe the first characters that I as a Young Adult, had first encountered.
Inspired by a Senegalese folktale, Redemption in Indigo by Karen Lord, I would classify as young adult fiction. It's sophisticated enough for adults, has adult ideas in it, but is a good introduction for young adults for adult thinking. Lord, has a knack for depicting characters that are well-rounded and enjoyable. I derived, for lack of a better word, a certain delight in the depiction of the undying ones - not so much spirits as creatures outside of time and space. They were more archetypes than characters, I think.
In all, even though it was set, not quite in our world, but a close enough world, and primarily in the dry savanna landscape of Senegal, it still evoked that warm visual memory I get from those grey, drab, overcast late spring days.
A fun little repast of a book.