Use Similar Colors to Denote Relationships
When similar (but not identical) colors are used, the suggestion is one of
relationship, with the degree of color similitude denoting the strength of the relationship. Colors of varying hue and saturation are therefore used very effectively to organize elements within any type of hierarchy. Navigating the chapter/section/sub-section hierarchy within a text, for example, is much more natural for the reader if this type of color coding is used. In hypertext, such coding can be used effectively to denote the proverbial trail of breadcrumbs leading back from multiple branching.