根据复分解反应发生的条件可以得知，蓝色的硫酸铜溶液与氢氧化钠 溶液 反应生成硫酸钠和 氢氧化铜 沉淀，由于该反应是在溶液中进行的，所以生成的是无色的 硫酸钠 溶液和蓝色的氢氧化铜沉淀，故反应现象应当描述为:溶液变为无色，并有蓝色沉淀生成.

According to the conditions under which the double decomposition reaction takes place, the blue copper sulfate solution reacts with sodium hydroxide solution to form sodium sulfate and copper hydroxide precipitation. Since the reaction is carried out in the solution, the colorless sodium sulfate solution and the blue copper hydroxide precipitation are formed, so the reaction phenomenon should be described as: The liquid becomes colorless with blue precipitation.