根据理论与生产实践经验，印刷品最难控制的颜色就是灰平衡。灰平衡是在一定印刷适性下，黄、品红、青三原色版从浅到深按一定网点比例组合叠印获得不同亮度消色(白、浅灰、灰、深灰、黑)，即得到视觉上的中性灰的颜色，影响其因素很多，印刷使用的墨量、纸张、满版浓度、网点面积、叠印以及网屏线数，都会对灰平衡产生千丝万缕的影响，这是最考验机器的套印精度及操作人员技能水平的。
According to theory and production practice, the most difficult color to control in printing is grey balance. Grey balance is to get different brightness achromatic (white, light grey, grey, dark grey, black) by the combination of yellow, magenta and cyan primitive color plates from light to deep according to a certain dot ratio. That is to say, the color of visual neutral grey can be obtained. There are many factors affecting the color, such as the amount of ink used in printing, paper, the concentration of full plate, dot area, overlay printing and the number of screen lines. Heng has a myriad of influences, which is the most testing machine overprint accuracy and operator skill level.