The dream was never George's anyway - it was Lennie's. It was George's way of soothing Lennie, of reassuring him that George would not leave him. George equally needed the fantasy to give him a reason to stay with Lennie. It provided a bond between them, but always had tinges of unreality about it (remember the coloured rabbits?). George's 'real' dream was epitomised in the small insight into an equal, true friendship which he experienced with Slim: a man who could really respond to him, share his burden and offer him real comfort.
George's dream with Lennie was merely a bedtime story to placate a childlike imagination. It was a story they shared like any other fairytale. The practical plans to attain the farm with Candy's money only occured after George and Lennie decide they do not want to stay at the ranch, with the threat of Curley and his 'jail bait' wife. George knows they are running out of options for work as Lennie has cost them many jobs. Sending Candy and Lennie ahead to set up the farm once they have paid the deposit is as impossible and ridiculous as 'red rabbits and blue rabbits and green rabbits.'