in a machine for molding colored plastic foam material , a cleaning cycle is performed , before changing color , to clean a feed circuit having a reservoir and interposed , in the machine , between a storage bin and a mold ; the cleaning cycle including : emptying the reservoir by suction to remove any material still inside the reservoir ; injecting compressed air into the feed circuit so that any material remaining along the feed circuit is at least partly expelled from the feed circuit and at least partly fed into a header located at the bottom of the reservoir ; and emptying the header by suction .