What does purple refer to in Emily Dickinson's poem "a solemn thing - it was I said"?

A mystic and spiritual color, and a favorite of the
creative and eccentric poet, Emily Dickinson, purple in the poem "A solemn thing--it
was--I said--" symbolizes the relgious depths that the speaker contemplates, and is,
thus central to the controlling metaphor of the comparison of the mundane life, the
"small," to the "hallowed thing," the holy, mystical, and spiritual
life.

As the speaker considers what a "solemn thing,"
a grand and impressive act, it is to become consumed in the eternal life, she realizes
that there is a vagueness to this mystical vision in its purple depths.  And, then
comparing the daily life to this abstruse spiritual vision, the speaker decides that for
her daily life triumphs over the mystical life and she
"sneered--softly--'small'!"