The “hues” in acrylic lines have been added to the colour line-up to take the place of pigments that a re either unavailable, incompatible with water-based emulsions, or are price prohibitive. Some pigments that are too fugitive to be included in an artist-grade paint line are replaced by a permanent pigment or blend. In other instances the reasons are health related. For example, Naples Yellow is a lead-antimonate pigment with excellent permanence, however it is highly toxic. A mixed Naples Yellow Hue now replaces this obsolete colour.