Are fashion designers feeling the economic downturn? Not so much — the Pre-Fall collections are abundant. While some may be scaling down and rejigging their businesses, many are keepin' on delivering us fanciful Pre-Fall collections. And thank goodness — how else would fashion followers survive these hard times? Optimism is a must have. As far as the clothes go, bright colors are aplenty, silhouettes are relaxed, and it's all about jackets and retro references. Take Zac Posen's parlor-presented collection: '50s flavor and Parisian prettiness. Preview on . . .