The term 'yellowish-brown pigment' can be described by two crossword solutions: SIENNA (6 letters) and OCHRE (5 letters). SIENNA is a natural earth pigment composed of clay and iron oxide, while OCHRE is a natural pigment composed of clay and hydrated iron oxide. Both pigments have been used since prehistoric times for painting and dyeing. They are also used in modern times for art, cosmetics, and industrial applications.