Add Flutter Colors

@@ -24,7 +24,27 @@ class PdfColor {
   final double g;
   final double b;
 
-  static var black = PdfColor(0.0, 0.0, 0.0);
+  static const black = PdfColor(0.0, 0.0, 0.0);
+  static const white = PdfColor(1.0, 1.0, 1.0);
+  static const red = PdfColor(0.95686, 0.26274, 0.21176);
+  static const pink = PdfColor(0.91372, 0.11764, 0.38823);
+  static const purple = PdfColor(0.91372, 0.11764, 0.38823);
+  static const deepPurple = PdfColor(0.40392, 0.22745, 0.71765);
+  static const indigo = PdfColor(0.24705, 0.31765, 0.70980);
+  static const blue = PdfColor(0.12941, 0.58823, 0.95294);
+  static const lightBlue = PdfColor(0.01176, 0.66274, 0.95686);
+  static const cyan = PdfColor(0.0, 0.73725, 0.83137);
+  static const teal = PdfColor(0.0, 0.58823, 0.53333);
+  static const green = PdfColor(0.29803, 0.68627, 0.31372);
+  static const lightGreen = PdfColor(0.54509, 0.76470, 0.29020);
+  static const lime = PdfColor(0.80392, 0.86274, 0.22353);
+  static const yellow = PdfColor(1.0, 0.92157, 0.23137);
+  static const amber = PdfColor(1.0, 0.75686, 0.02745);
+  static const orange = PdfColor(1.0, 0.59608, 0.0);
+  static const deepOrange = PdfColor(1.0, 0.34118, 0.13333);
+  static const brown = PdfColor(0.47451, 0.33333, 0.28235);
+  static const grey = PdfColor(0.61961, 0.61961, 0.61961);
+  static const blueGrey = PdfColor(0.37647, 0.49020, 0.54510);
 
   const PdfColor(this.r, this.g, this.b, [this.a = 1.0]);
 
@@ -47,4 +67,6 @@ class PdfColor {
           (((g * 255.0).round() & 0xff) << 8) |
           (((b * 255.0).round() & 0xff) << 0)) &
       0xFFFFFFFF;
+
+  String toString() => "$runtimeType($r, $g, $b, $a)";
 }