October along the Clipper City Rail Trail is all rust and brick, the old line running straight through Newburyport while the maples above it let go a little more each day. Paiva & Sons Landscaping Corp. works both ends of that turn. Through the warm months it is mowing on a set rotation, trimmer work along the fence lines, edges cut so clean they read like a drawn line; through autumn it is cleanups, leaves off the turf before the first hard frost pins them there. Then winter, and the plows go on — driveways cut to the pavement, front walks cleared, whatever the storm piled up moved out of the way of an ordinary morning. The city changes color four times a year and the trucks change with it.