The colors indicate percent of sugars in the low range (blue, default definition is less than 80 mg/dL), percent in the target range (green, default 80 mg/dL - 130 mg/dL), and high (red, default is greater than 130 mg/dL). This target range is at odds with the 80-140 default target range in the hourly statistics graph, but perhaps I am mistaken in one or the other. You can customize the target range.
The pie charts break the readings down by time of day in the following categories: All day totals, early morning, before breakfast, after breakfast, before lunch, after lunch, before dinner, after dinner, and late evening. You can customize the hours for each of these categories. Categories can overlap. You can also create new categories. For instance, I was able to create a category called "Pre-dawn phenomenon" and define it as the hours from 11:00 pm - 4:00 am.
The bar chart on the right shows the percent of total readings for the specified time period by glucose category. Default categories are less than 40-55, 56-70, 71-100, 101-130, and so on. I don't think these categories can be changed.
You can choose to display statistics for any number of consecutive days, or types of days, for instance weekeneds or Mondays. You can even select groups of days, like "Tuesdays and Thursdays".