Add PdfColor.shade

@@ -7,6 +7,7 @@
 - Improve Internal data structure
 - Improve Internal data structure
 - Remove deprecated functions
 - Remove deprecated functions
 - Optimize file size
 - Optimize file size
+- Add PdfColor.shade
 
 
 ## 1.5.0
 ## 1.5.0
 
 

@@ -141,6 +141,17 @@ class PdfColor {
     return 0.2126 * R + 0.7152 * G + 0.0722 * B;
     return 0.2126 * R + 0.7152 * G + 0.0722 * B;
   }
   }
 
 
+  /// Build a Material Color shade using the given [strength].
+  ///
+  /// To lighten a color, set the [strength] value to < .5
+  /// To darken a color, set the [strength] value to > .5
+  PdfColor shade(double strength) {
+    final double ds = 1.5 - strength;
+    final PdfColorHsl hsl = toHsl();
+
+    return PdfColorHsl(hsl.hue, hsl.saturation, hsl.lightness * ds);
+  }
+
   /// Get a complementary color with hue shifted by -120°
   /// Get a complementary color with hue shifted by -120°
   PdfColor get complementary => toHsv().complementary;
   PdfColor get complementary => toHsv().complementary;