Recall that the legend is that Gene Rodenberry was initially against casting Patrick Stewart as Picard because Stewart wasn't French! Better for casting directors to be vague and non-specific about a characters description, and see who gets the part right.
Also the security chief was called "Macha" Hernandez until they decided to cast a pale blond woman in the role and changed her name to Tasha Yar -- and Data was supposed to be Asian or Pacific Islander in appearance. In DS9, the doctor was going to be Julian Amoros until they cast Siddig el Fadil (as he was then known) in the role and changed the character's surname to the Arabic "Bashir."
And of course Ripley in Alien
was written as male -- or rather, all the roles were written as gender-neutral and the producers cast accordingly.