Well I disagree on that.
Weren't most of the TOS vulcans played by rather dark actors.
I'm not talking about actors' hair and eyes. The script specifies
"her skin is fair", and therefore (green-eyed) Kirstie Alley didn't get the routine application of Max Factor blend of Vulcan pancake,
LN1 ("Leonard Nimoy 1"), specially formulated for Fred Phillips during the early days of TOS).
Lawrence Montaigne and Mark Lenard played both Romulans and Vulcans in TOS, anyway. I didn't see that they were given lighter makeup treatments in "Balance of Terror" than they received for "Amok Time" (Stonn) or "Journey to Babel" (Sarek). As far as I know, the Romulans got LN1 as well.
And I did read interviews with ST II's makeup guy, Werner Keppler, who had to be schooled in the art of Vulcan makeup application by Leonard Nimoy, because Fred Phillips had become legally blind (not long after TMP). Keppler
did not know the backstory on Romulans. When he was asked to provide green blood for Spock's death scene, he totally misunderstood and whipped out a green pancake makeup and liberally applied it to Nimoy's hand! Then, they ended up going back to the makeup area and Keppler mixed up a green coloured gel-like makeup, to pass as Vulcan copper-based blood, instead.
And i rather doubt Sowards script description got to the final draft phase without Bennett noticing that line.
The line is
in the final shooting draft; of course Bennett noticed it! He probably agreed on the look of Alley's eyebrows.