button add null color

lib/common_widgets/aku_material_button.dart

@@ -29,8 +29,8 @@ class AkuMaterialButton extends MaterialButton {
     this.padding = EdgeInsets.zero,
     @required this.child,
     this.color = Colors.transparent,
-  })  : nullColor = color.withOpacity(0.5),
-        super(
+    this.nullColor = Colors.transparent,
+  }) : super(
           key: key,
           onPressed: onPressed,
           elevation: elevation,
@@ -46,6 +46,7 @@ class AkuMaterialButton extends MaterialButton {
           ),
           child: child,
           color: color,
+          disabledColor: nullColor,
           materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
         );
 }