How to define the expression rule for site accent color? what should we consider for decisioning?

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How to define the expression rule for site accent color? what should we consider for decisioning?

As per the system, 

The accent color is used to highlight key interface elements. Avoid grayscale colors (black, white, and gray) that are similar to colors used for interface elements and green/red that are similar to colors used to indicate positive/negative values
If I want to conditionalize the colors for links, grid row highlight, etc, how should we define the conditions?

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