”Culoarea piersicii este portocaliul” would be considered acceptable by many Romanians. It is debatable if here ”portocaliu” is an adjective or a noun.
Why is it piersicii instead of piersiciei? Thank-you.
This is a common mistake in Romanian. An easy rule of thumb to build dative case for feminine nouns in romanian is to add "i" to the PLURAL nominative form. So piersică (sg) - piersici (pl) -> piersicii