diff --git a/lib/ansicolor.dart b/lib/ansicolor.dart
index 83feff1..481db0f 100644
--- a/lib/ansicolor.dart
+++ b/lib/ansicolor.dart
@@ -53,17 +53,17 @@ class AnsiPen {
   /// attributes.
   String write(String msg) => "${this}$msg$up";
 
-  black({bool bg: false, bool bold: false}) => _std(0, bold, bg);
-  red({bool bg: false, bool bold: false}) => _std(1, bold, bg);
-  green({bool bg: false, bool bold: false}) => _std(2, bold, bg);
-  yellow({bool bg: false, bool bold: false}) => _std(3, bold, bg);
-  blue({bool bg: false, bool bold: false}) => _std(4, bold, bg);
-  magenta({bool bg: false, bool bold: false}) => _std(5, bold, bg);
-  cyan({bool bg: false, bool bold: false}) => _std(6, bold, bg);
-  white({bool bg: false, bool bold: false}) => _std(7, bold, bg);
+  void black({bool bg: false, bool bold: false}) => _std(0, bold, bg);
+  void red({bool bg: false, bool bold: false}) => _std(1, bold, bg);
+  void green({bool bg: false, bool bold: false}) => _std(2, bold, bg);
+  void yellow({bool bg: false, bool bold: false}) => _std(3, bold, bg);
+  void blue({bool bg: false, bool bold: false}) => _std(4, bold, bg);
+  void magenta({bool bg: false, bool bold: false}) => _std(5, bold, bg);
+  void cyan({bool bg: false, bool bold: false}) => _std(6, bold, bg);
+  void white({bool bg: false, bool bold: false}) => _std(7, bold, bg);
 
   /// Sets the pen color to the rgb value between 0.0..1.0.
-  rgb({r: 1.0, g: 1.0, b: 1.0, bool bg: false}) => xterm(
+  void rgb({r: 1.0, g: 1.0, b: 1.0, bool bg: false}) => xterm(
       (r.clamp(0.0, 1.0) * 5).toInt() * 36 +
           (g.clamp(0.0, 1.0) * 5).toInt() * 6 +
           (b.clamp(0.0, 1.0) * 5).toInt() +
@@ -71,10 +71,11 @@ class AnsiPen {
       bg: bg);
 
   /// Sets the pen color to a grey scale value between 0.0 and 1.0.
-  gray({level: 1.0, bool bg: false}) =>
+  void gray({level: 1.0, bool bg: false}) =>
       xterm(232 + (level.clamp(0.0, 1.0) * 23).round(), bg: bg);
 
-  _std(int color, bool bold, bool bg) => xterm(color + (bold ? 8 : 0), bg: bg);
+  void _std(int color, bool bold, bool bg) =>
+      xterm(color + (bold ? 8 : 0), bg: bg);
 
   /// Directly index the xterm 256 color palette.
   void xterm(int color, {bool bg: false}) {