Iron oxide, pigment, colored, color pigment, exposed concrete, pigment powder

Iron oxide stands for:
Rust, mixture of various iron oxides
Collective term for various pigments, see iron oxide pigment
Iron(III) oxide, Fe2O3
Iron(II,III) oxide, Fe3O4
Iron(II) oxide, FeO
Iron(I) oxide, Fe2O

source: en.wikipedia.org/wiki/iron-oxide