Luminosity discharger
The luminosity discharger was a device, typically appearing in twos, atop the dome of a Dalek's casing. They would light up whenever a Dalek spoke. (PROSE: Prisoner of the Daleks)
Ace used a baseball bat enhanced by the Hand of Omega to destroy the right luminosity discharger of an Imperial Dalek. (TV: Remembrance of the Daleks)
The red Supreme Dalek of the New Dalek Empire was distinguished by having three luminiosity dischargers. (TV: The Stolen Earth/Journey's End)
Size
Early Daleks had small, bulb-shaped luminosity dischargers. (TV: The Daleks et al.) The Supreme Dalek of the Supreme Council was distinguished by its larger luminosity dischargers. (TV: Planet of the Daleks)
Daleks of the Last Great Time War and beyond, including the New Dalek Paradigm, had large luminosity dischargers of a size which had previously only been sported by the Supreme Council. (TV: Dalek, Victory of the Daleks)
Colour
As well as size, the Dalek Supreme of the Supreme Council was distinguished by the purple colour of its luminosity dischargers. (TV: Planet of the Daleks)
Imperial Daleks seen in the Shoreditch Incident had golden luminosity dischargers. (TV: Remembrance of the Daleks)