shade, tint, tone

features, lineaments, looks

countenance, face, visage

distinctiveness, distinctness, individuality, singularity, uniqueness

attribute, characteristic, earmark, essentiality, feature, flavor, hallmark, mark, point, property, savor (also savour), stamp, trait

disposition, grain, sort, temper, temperament

composition, makeup

essence, essentiality, interior, interiority, soul, spirit

metal, stuff, substance

habit, way