Final answer:
The color blue in a bar graph typically represents a specific category within the data, such as a life stage in a demographic study. It allows viewers to visually compare proportions and understand the composition of different age groups or other data segments.
Step-by-step explanation:
When a bar in a graph is colored blue, it often signifies a specific category or type of data that the graph is representing. In the context of age distribution or demographic information, a blue bar might represent a particular life stage of people within an age class. For example, in a bar graph showing the U.S. age distribution, different colors within a bar might indicate age groups such as children, adults, and seniors. If the blue color represents one of these groups, then each segment of blue within a bar would convey how much of that age class is made up by the corresponding life stage. It's a visual way to compare proportions and understand the composition of different age brackets over time or across different criteria like regions, average life span, or income per person.