At this point, there isn't much variety in the coloring of objects just blue and black. That's because the default color scale doesn't have enough range to show subtle differences in activity levels in this particular execution. You can recalibrate the color scale so that only the most active object is colored red, with less-active objects taking on a broader range of colors. Now you will see that some of the classes and objects have turned red, pink, violet, or purple, with redder colors signifying more activity. Note also that the number at the right end of the legend the maximum base time value is much smaller than it was initially.
Base time is just one of several coloring criteria.
You can also view various dependencies between objects. Who Creates Object from the resulting menu. The red line shows the creator of this object. Select Who Calls Object . Zero or more green lines show the callers of this object.