Zone markings should be conspicuous and distinctively different for different zones (see Figure 1.10).
Additional Information:
Zone marking should not interfere with reading of quantitative markings. Differently colored bands are often used to indicate, e.g., the normal operating range, upper/lower limits, and danger range of a parameter. If color is used for coding, color should be related to meaning (see Guideline 1.3.8-5).
Figure 1.10 Zone markings.