And while the costumes are a major data point…they’re not infallible. Besides, she doesn’t switch to all black (in my mind) until Leopold dies. Then there’s that exchange with (was it the mirror?) where she says she simply finds that black suits her.
She switched permanently to black when Leo dies. Before then wearing all black was a private thing to indicate her darkening heart and her tend toward loving magic.
Regina used her EQ voice when she told Tinkerbell to leave and she definitely began having dark thoughts about Snow without being horrified by them. I would say this was probably after the Doctor because Rumple said to bring her anger to the next lesson whereas she wasn’t angry when we saw her in the Doctor.
But voice was only the EQ voice for the last few seconds of her interaction with Tink. Before then she had “young Regina” voice. Then after Tink left she probably switched back because this was her first big step toward becoming full time EQ