How to: Color TreeMap Using the Palette Colorizer
To color TreeMap using a Palette, assign a TreeMapPaletteColorizer object to the TreeMapControl.Colorizer property. To color all group items using one color, set the TreeMapPaletteColorizer.ColorizeGroups property of the colorizer to true. To specify a palette that should be used to color items, assign an instance of the Palette derived class to the TreeMapPaletteColorizerBase.Palette property of the colorizer.
A complete sample project is available at https://github.com/DevExpress-Examples/how-to-manually-populate-treemap-with-data-t360867