XMLBlueprint

XMLBlueprint is the smart XML Editor for Windows with full support for DTD, Relax NG, Schematron, XSD (XML Schema), XSLT (1.0, 2.0, 3.0) and XPath (1.0, 2.0, 3.0).

Syntax Coloring is supported for XML documents, but also for HTML, CSS, Java and JavaScript files. You can customize the text colors and the background colors.