Can I dye a butterscotch color leather ottoman black to game my couch?
Answers: Depends. Most leather couches use leather that is not actually suntanned, but basically sprayed with vinyl, much as how most sneaker leather is finished. If yours is of this type, you can't dye vinyl. If your leather is truly brown, you probably could. Find an inconspicuous spot, and see if you can scrape off a vinyl blanket. If your scraping seems to walk right into the leather, like if you scraped a high-quality work boot, you may be correct to go.
You could, but why bother and the possibility of ruining the leather. When it's a lovely colour which will match anything. Why not buy one of those cushions next to slip proof bottoms to put on top of it, they also come in black.