(FORTUNE Magazine) – After three years of seesawing on hemlines and flirting with blue-collar grunge and dreary, shapeless clothes that epitomized the so-called waif look, America's fashion designers are rediscovering their bread and butter: businesswomen. "We lost our influence, and to some extent our credibility, because good wearable clothes were unavailable,'' admits veteran designer Bill Blass, whose clients include Barbara Walters and Linda Wachner. "Now we must prove to our clients that we are paying attention to their needs." Last month on the fashion runways of Manhattan (no, not Kansas), designers showed off their Spring '95 collections, an array of snappy suits, dresses, and ensembles that could be worn by real women -- a simple dress with a matching coat or jacket, for example. Office-friendly fashions first made a comeback in the Fall '94 collections, and some designers, like Blass, are now reporting retail sales increases of 30% or more. To keep the momentum going designers are opting for curvy suits and upbeat palettes. Pink is the color for spring, but yellow, blue, scarlet, tangerine, and black and white checks also make the cut. "Executive women want suits with some authority, and these clothes have a strength that had been lacking for several seasons," says Neiman Marcus fashion director Joan Kaner. Designers are now combining glamour and utility. Under their refined suits, runway models showed lacy bustiers and shiny halter tops. That's the glamour. When the jacket stays closed, the outfit is demure enough for everyday office meetings; for a more intime dinner, the busy executive simply unbuttons