Index: wp-testlib/base.php
===================================================================
--- wp-testlib/base.php	(revision 289)
+++ wp-testlib/base.php	(working copy)
@@ -523,7 +523,7 @@
 	#return PHPUnit::run($suite);
 	$result = new PHPUnit_Framework_TestResult;
 	require_once('PHPUnit/TextUI/ResultPrinter.php');
-	$printer = new PHPUnit_TextUI_ResultPrinter(NULL,true,true);
+	$printer = new PHPUnit_TextUI_ResultPrinter( NULL, true, $colors = !((bool) stristr(PHP_OS, 'WIN')) );
 	$result->addListener($printer);
 	return array($suite->run($result), $printer);
 }