Index: src/includes/admin/admin.php
--- src/includes/admin/admin.php Base (BASE)
+++ src/includes/admin/admin.php Locally Modified (Based On LOCAL)
@@ -634,6 +634,11 @@
 	 */
 	public function register_admin_style () {
 
+		// Color schemes are not available when running out of src
+		if ( false !== strpos( $GLOBALS['wp_version'], '-src' ) ) {
+			return;
+		}
+
 		// RTL and/or minified
 		$suffix  = is_rtl() ? '-rtl' : '';
 		$suffix .= defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '' : '.min';