We need to measure for Gray Balance because each person's individual perception of color is different. Each person has subconscious preferences that influence their color judgement. The human eye can detect any shift in neutrality when neutral areas are compared side by side. Comparing just by looking at the neutrality of two gray scales is much easier than comparing the purity of the reproduced process inks with a color in the original. The eyes can quickly detect if there is any color cast in the neutral area. In this respect, the eyes become the most sensitive instrument for checking gray balance. We are all influenced by variables in our environment that we are usually not aware they exist. To illustrate this, compare the two greens in Figure