Dome

The dome was the top part or "head" of a Dalek's casing, upon which the eyepiece was mounted. At GeoComTex, the Ninth Doctor instructed security personnel to aim for the "Metaltron's" dome, specifically the eyepiece. (TV: Dalek) Similarily, the Fifth Doctor instructed British Army soldiers to aim for the eyepiece, "the stalk at the top of the dome". (TV: Resurrection of the Daleks)

As a distinguishing feature
Typically, the domes of most Daleks matched the majority of their casings. (TV: The Daleks et al.)

Across Dalek history, the Emperor's Personal Guard were distinguished by their black domes. (TV: The Evil of the Daleks, The Parting of the Ways)

As well as a black dome, the Dalek saucer commander was distinguished by alternating black-and-silver panels on the base unit. (TV: The Dalek Invasion of Earth)

During the Last Great Time War, members of the Dalek Scientific Division were distinguished by their blue domes. (AUDIO: A Thing of Guile)

Individual cases
As a result of his incursion to retrieve Davros from the time-locked Last Great Time War, Dalek Caan lost his dome as well as a substantial portion of his casing. (TV: The Stolen Earth)

The dome of a red Supreme Dalek was seen at UNIT's Black Archive in the 2010s. (TV: The Day of the Doctor)