Colors should be chosen for maximum contrast against the label background.
Additional Information:
Table 11.2 rates various color combinations in terms of relative legibility. To ensure adequate contrast and prevent loss of readability because of dirt, dark characters should be provided on a light background. If colored print is used for coding purposes, it should conform to the established color coding scheme for the control room (see Section 1.3.8, Color).
Table 11.2 Relative legibility of color combinations.