It occurred to me while reading a discussion of race in fiction that I almost never imagine the faces of characters in books that I read. I do recall my perception of Scalzi's Fixer Young changed from white to black as he introduced the new tidbits about the character, but if you asked me to describe my favorite characters from books I've read numerous times (even characters I have crushes on!) , I would be making it up as I went along. The only recent occasion I can recall attempting to visualize a character and assign a race was when a character with an usual name was introduced in this book and I had to make up my mind whether the person was East Asian or African.
At some point I took an online quiz that implied that an inability to visualize faces in this way indicates some sort of non-neurotypical brain issue, but for the present it just makes me really terrible at playing the "cast this hypothetical film adaptation" game.