Below is an example pulled from Census.gov email newsletter, showing proper and inproper use-case scenarios. Azul 700 and PMS Blue are different colors, but similar enough in hue and value that it’s important to clearly differentiate between the two by taking advantage of Primary and Secondary layouts.
Special Use Case CTA:
Primary vs. Secondary
“Special Use Case CTA” buttons are represented by Azul 700, while “Engage with Site Content” uses PMS Blue.
Because of the similarity of their hue and value, it is important for one of the categories to use their secondary layout when both buttons are being used in close proximity to one another.