Starting tonight, look at One Rincon Hill to get your weather forecast. The top of the city's tallest apartment building will now use a nifty color-coded system of lights to signal the weather. Red: warmer weather ahead; blue: colder weather; green: 50-percent or more chance of rain; and amber: no change. The beacon will turn on at dusk every evening and will remain on all night. Using tall buildings as weather beacons is somewhat of a tradition. Syracuse, N.Y; Minneapolis; Dubuque and Des Moines, Iowa; Bismarck, N.D.; Toronto; and in two buildings in Brisbane and Adelaide, Australia have beacons. This is the Bay Area's first.