Common mistakes include choosing colors that blend too closely with vinyl siding or selecting insufficient contrast, causing the house to appear flat. Another error is ignoring the undertones of vinyl siding, often warm cream or beige. Choosing too many exterior colors overwhelms small cottages. Overusing bold colors across large surfaces or failing to test samples in varied light leads to unsatisfactory results. Limiting colors to two or three, emphasizing contrast, and understanding undertones prevents these errors.