Emily Dickinson was a very spiritual poet and the colour purple has inferences for Christianity as well as for the theme of this poem - Royalty. Emily Dickinson may be trying to link the idea of inherited kingship with that of the suffering it also (sometimes) carries inherent in its privilege, The colour purple was important to the Romans in terms of the class/education/civil rights of the toga-wearer and it also has symbolism in Christianity today. As well as being the colour of royalty, it is the colour of the blood of Christ which is central to the wine in the chalice of the Roman Catholic Mass - it is also the colour of bruises and martyrdom - some people see it as the colour of the victim as well as that of the victim. The trinity is also important because it ties together the idea of a 'king' (Christ the King/God) with that of a defenceless victim or martyr who gave his life for others. In the case of Christianity, it was to save souls from sin and thus guarantee them entry to eternal life with Christ in heaven. Emily Dickinson may be saying,among other things, that, the role of king is one of privilege, power, pomp and ceremony but that it also carries heavy responsibilities when carried out properly - responsibilities that can be as heavy as the heavy cross borne by Jesus Christ for the sake of his followers. We also remember the crown of thorns and its bleeding, and the spear in the side of Christ on the cross. Suffering would have been a familiar theme for Emily Dickinson and other Christians of her time as it ties in with the ideas of self-sacrifice, forebearance, never complaining, patience, unconditional love and charity, unselfishness and prayer.
i simply wish to say that purple is always associated with finality or solemnity.emily has rightly said none can avoid this purple.
it is the color of rituals.
i think i have said enough for one to understand the color purple used by emily.