i agree!
i would also recommend u wear colors that look like the newest launch on counter, so they can see that u are aware of all the happenings with MAC.
and if ur unsure on how dramatic to go, my suggestion would be to go see how the current employees wear their makeup. i say this because when i interviewed for MAC i tried going in with different looks depending on which location i was interviewing for. some counters wear a more "beauty culture" type of look, which is very polished/natural looking "red carpet" type of makeup. and there are other counters that are more extravagant or dramatic with their makeup. it all depends on the store's demographic.
u still want to do YOU, but keep in mind that u want them to invision u as a part of their team.
and yes DO wear 100% Black clothing!
be yourself, ur makeup skills rock! show them ur passion for the art & how u would love to teach others. their really big on teaching