Hmm, in light of learning about the basic black wardrobe I definitely vote for color. I was going to say red cardigan because it is a power color. I think it is more about business at this point. You want to be taken seriously and this is a business setting. I wouldn't go all floral, seems to wishy washy.
Perhaps a good compromise would be a new feminine top in a lovely color, whatever suits your coloring best. And if you can swing it, a pair of colorful shoes to match. With the black pants/skirt it will be professional but flattering. (And if you can stand them, pointy toe shoes always seem serious and sexy to me.)
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