Simply right-click on the cross-tab and choose Cross-Tab Expert. THere are tabs that let you modify all aspects of the cross-tab. You can choose a certain style, or click on Customize Style to set more granular properties (such as color).
I have an entire chapter dedicated to teaching you how to build cross-tabs and modify their properties in my Encyclopedia book. You can find out more about my books at
Amazon.com or reading the
Crystal Reports eBooks online.