What determines whether the printer (HP Photosmart 7520) uses photo black or regular black?

I have an HP Photosmart 7520 that I use as my everything printer. I never used it for printing Photos, but I'm getting older now and thought maybe it would be nice to have a few Photos. Normally I just put in Magenta-Blue-Yellow-Cyan, and I print a lot of flyers for work, so I use offbrand ink I buy on amazon and its actually really cheap. I thought about getting an ecotank, but I can't see buying a $200 printer to save on ink when I spend only about $100/yr on ink. Plus the Photosmart has a feed scanner, which is useful for scanning legal work. I don't really have a spot to have one printer f

Question by Trent Tompkins on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.