Highlighting is more relative than absolute
Non-designers often don't realize that the style of highlighting is much less important than the relationship between the highlights and non-highlights.
There are all kinds of approaches to creating highlights. One might use font-color, background-color, size, font variation (e.g. italics, underlining) and weight (e.g. "boldness") to create a highlight:
But, what matters more than the specific highlight approach is the relationship between that highlight and the surrounding text:
- How frequently the highlight(s) appear
- How much contrast there is between the highlight and the surrounding text (the greater the difference in font size/weight/color/etc the more prominent the highlight.
Generally, highlighting should similarly to the same way lighting is used in a home, office or a museum:
In some physical areas (e.g. museum) you will want to highlight specific items, so it makes sense to spotlight the item and darken the surrounding area. This is an example of a prominent, high-contast highlight.
In other environments (e.g. a workspace) where the user needs to perceive and interact with the entire space without unnecessary distraction, you want to use even lighting to illuminate everything equally and neutrally.
These common-sense principles can be similarly applied to determining the frequency, distribution and prominence of highlighting in text. Some texts (e.g. a novel) don't use highlighting because it can distract the user from the journey/flow of the text. Other texts (e.g. business papers) can use highlighting effectively to spotlight key concepts for busy/distracted/speed readers.
Here is a simple example that shows that the highlight relationship is more important that the particular highlighting style.
In the first example, the highlighted text is colored, bold, italicized and background-colored, but since the rest of the text is also styled similarly, the highlights don't particularly stand out.
In the second example, the highlighted text has only ONE variation: it's size. There is no other coloring, weighting, etc. But since the surrounding text is plain and the frequency of highlights is low, the highlights stand out much more clearly and legibly.