“Then the Brahmanas (present there), their expectations fully gratified, bestowed names upon the new-born pair, they said 'Let this son of king Drupada, be called Dhrishtadyumna, because of his excessive audacity and because of his being born like Dyumna (glory) with a natural mail and weapon.' And they also said, 'Because this daughter is so dark in complexion, she should be called Krishnaa ( the dark one).”
Source :— Adi Parva, Chapter 155.
See?
And Arjun himself admits about his name being Krishna.
And Krishna, my tenth appellation, was given to me by my father out of affection towards his black-skinned boy of great purity.'
XLIV Virat Parva.
And I did not find any reference of Subhadra being called as Krishnaa.