Blue has the feeling of a cold spring morning when hoarfrost covers the daffodils. To a little more concrete, it's a cardamom-rich woody scent with green and floral notes. The only other perfume I've found with a similar "feel" was Frederic Malle's L'eau D'Hiver, but the notes are quite different. My only complaint is the scent strength, which is much closer to an EDT than an EDP.
It's been repeatedly backordered at the one (well-known) niche perfume shop that carries it ... there's a reason for that. Blue is unique.