Pie charts can be used when you need to represent a value as part of a whole. It is commonly used to represent percentages, relative magnitudes or relative frequencies. If your intent is to compare a particular value (slice) against the whole of the Pie chart, then it can be quite effective. If however you want to compare two seperate segments, then it can get more difficult. If this is the case, you may want to consider bar charts or perhaps line charts.
The colours can be customised, as can the borders (using the same color as the background. The charts can also have a drop shadow if you want one.