NEW YORK — What’s tried and true, and in all shades of blue? It’s denim, of course, and the fabric was all over the runways for spring. Anna Sui, for example, chose a faded version for a long jeans skirt with studded details. Paired with a flower-trimmed crocheted cardigan, it’s a look that brings to mind the days of love-ins and sit-ins. For more, see pages 8 and 9.