Hostess: Lynette Walden.Three half-hour dramas, based on 1940s-type murder mysteries, display adventurous programming and showmanship. Of the three airing in August — there’ll be three more in September — one’s overdone, another’s strong and the third is commercial. But they’re all alternative programming in an area in which TV is financially or creatively anemic. Programs, shown on succeeding Sundays, forsake black-and-white authenticity for color. In all three, production designer Armin Ganz inventively uses L.A. sites.