I made a very good pale ale using Grape Nuts. Very big creamy head, good flavor. I remember using distilled water to brew, with no added salts, since I knew the cereal contained a lot of salts already.
If experimenting with cereals, I would stick with the basics. Grape Nuts are yummy, they already contain barley malt so it's a good fit. Shredded Wheat. Regular Life cereal. Corn Flakes. Rice Krispies. All these might turn out okay.
But anything more like Lucky Charms, Fruity Pebbles etc..... blecch, that's going to turn out a gray color, and yeah, really just a gimmick.
Hold back on salt additions. You might only need distilled/RO plus acid to get the pH down where it belongs.
Or... just don't brew with cereal at all.