fjn-
I was a little puzzled by the texture of the masonry units since they did in someway look like a clay product that had sand in it, but it also looked like a concrete product the had a very fine texture that could hold a lot of water during manufacturing without bulging.
The apparent "motar beds" on the inside of the face shell and the "hand holds" on the webs core look like those common in many concrete products. I do not know of many clay products that tapered cores since they are extruded, but a cast, pressed brick could have contoured cores.
The color would come from the clay deposits, while iron oxides can be used for and permanent color in concrete products.
Indiana does use a lot of brick because of it location in comparison the concrete products. Whatever material, it looks like a part of a quality wall.