I would like to change the look and feel of the xamRibbon control in WPF based windows application according to our color concept.
How to customize the existing theme and how to apply that theme for the ribbon control?
You should take a look at the samples in the feature browser. There are several that involve changing the color scheme of the xamRibbon. The samples in question are those that start with "Samples\XamRibbon\RibbonScriptWash_" or when you run the sample look under xamRibbon->Themes and Custom Styles.