Hmm....I think of J. Crew as sort of "deconstructed preppy," or "messy preppy" which is kind of traditional prep with an urban/equestrian edge. The sales ladies I see at J. Crew are usually wearing some kind of woven button down tucked into a skirt with knee high boots or ankle socks and heels, and they are wearing a lot of accessories to keep it from looking too "school girl." The button down doesn't have to be white, it can be any color. I know you don't usually wear woven button downs, so maybe you could layer a cardigan over a knit top, and tuck the bottom layer into a skirt with boots, or leave it untucked and wear it with pants of some kind, either nice, dark jeans tucked into boots, or slacks of some kind. Really, I would have fun with accessories if I were you. That's really what is most noticeable. So, maybe a few necklaces layered, or one big statement necklace (what about your pearls?), and do you wear hair accessories? If so, you may think about wearing a cute headband or barette or something like that.
Is that helpful? Is there anything else specific that you are wondering about?
If I were going to an interview at J. Crew, I would wear my bright orange/red pants, grey heels, grey and white striped knit top, and some kind of jacket over the top, probably the dark blue denim one. I'd also wear a cuff bracelet. Or, I'd wear my denim pencil skirt, nude microfishnet stockings, cream button down and the orange tweed jacket layered over it with a cognac skinny belt. Not sure which shoes I'd go with, I'd have to think about that.
