A Gantt chart is made up of four distinct areas.
Since a Gantt chart inherits all the usual properties of a JpGraph Graph() you have the access to the same method to formatting the image as before. For example to have a shadow around the image you call Graph::SetShadow() and to set the margin color you can use Graph::SetMarginColor(). Please refer to the reference documentation for a full list of supported features.
To create a Gantt chart you add objects to it. As of this writing you may add the following object by the use of the GanttChart::Add() method
All these objects may be extensively modified in terms of formatting. You can specify color (both fill- and frame color), size, titles, style and patterns and so on. All these objects comes with (in my mind) sensible default so you don't have to specify a lot of parameters. But if you need a fine grain control or if you disagree with my taste you can.