Heidi Weisel: This young native New York designer is known for her easygoing evening wear -- formal attire for the more laid-back set. For the first lady, she suggests a steel gray satin A-line evening skirt with a steel gray boat-neck sweater trimmed in satin piping and with faux-mink cuffs. Chelsea Clinton would wear a fitted, full-length brown satin skirt with a brown, sleeveless cashmere crew neck and a matching cardigan to wrap jauntily around her shoulders. Very modern.