I own nothing.
When she is especially young, considered too young to dress herself, Irissë wears blue. Blue and silver, for those are the colors of her father's house. They are the colors that her father wears, and her mother, and her older brothers. Irissë wears the same colors as them, always, and feels as though she will be forgotten there, a piece of scenery in the background. When her resemblance to her father is remarked upon, when it is remarked upon that her eyes are nearly totally blue, like her mother's, this feeling only deepens.
When she is considered old enough to dress herself by her mother, Irissë wears blue no longer. Much to the bewilderment of Nolofinwë and Anairë, their daughter, who has never complained about her clothes before, suddenly insists on wearing white instead of blue. When it comes to dresses, Irissë will wear nothing but white and silver. Her parents expect this to pass. Her brothers know better. So too do her cousins, and her grandmother.
The silver she wears out of deference to her father, her house. Irissë is not prepared to make a complete departure from her house's colors. Her young mind tells her that that would be unacceptable.
As for the white, if anyone asks (and few do), Irissë will say that she wears white to honor her grandmother, Indis. Indeed, Indis the Fair does wear white quite often, though not all the time, and it gives Irissë pleasure to see the expression of shocked gratitude that steals over her face. But that is not the whole reason that Irissë has chosen to wear white.
She needs… Well, Irissë isn't sure what she needs, not just yet. She does know what she wants, however. Irissë wants to not just be the daughter of Nolofinwë, granddaughter of the King. She is proud of her father, and proud of her grandfather, and will never let anyone think differently. But she wants to be a person whose identity is not predicated solely on who her father is, who her grandfather is. She is not nearly the granddaughter of the King, and the daughter of the second Prince. She is not merely the only granddaughter of Finwë Noldóran. She is Irissë. She is herself. She will not fade into the background like a piece of furniture or a tapestry.
So she wears white, and not blue.
Note: The colors of the House of Fingolfin appear to be blue and silver, and while I'm sure they deviated from that color scheme now and again, it appears to be the colors Fingolfin and his sons wore quite often as well. Yet Aredhel is remarked upon and never wearing any colors but white and silver. I take that to mean that she made a conscious choice to essentially never match up with the rest of her family, and I was curious as to why. Also, about that bit about her being Finwë's only granddaughter, Galadriel hasn't been born yet at this point in time in my (completely head-canon and not actual canon) timeline.
Irissë—Aredhel
Nolofinwë—Fingolfin