We have a housebroken cat as well, and it is unusual. Spooky arrived as a stray youngin' a couple of weeks before Halloween last year and, of course, she is solid black. She was so good with my infant granddaughter that I decided she would be a good outside cat, and I started to care for her and had her spayed.
So that she could stay in the garage when it was really cold, I put a litter pan out there. There is no way in the world that I was/am putting a litter box any further inside than that! Worked well ... she prefers to go outside, but used the pan just fine if she was confined to the garage.
After a month or two, my husband (the totally non-cat person) lets the cat in the house in order to create total entertaining chaos with the 2 dogs that have never been around a cat before.
Long story made shorter -- Spook goes to the door that leads to the garage and meows any time she needs to go out. She has never gone in the house, although she is in most of the time now. Greatest cat ever, IMHO.
Squire Tom is black also (Dad was in the 13th Air Depot WWII). Does Spooky “talk” as well? When He’s ‘calling me’ it sound similar to “where are you”!