added backgroundColor (initial)

lib/src/chart/bar_chart/bar_chart_data.dart

@@ -22,9 +22,11 @@ class BarChartData extends AxisChartData {
     ),
     FlBorderData borderData,
     double maxY,
+    Color backgroundColor,
   }) : super(
           gridData: gridData,
           borderData: borderData,
+          backgroundColor: backgroundColor,
         ) {
     initSuperMinMaxValues(maxY);
   }

lib/src/chart/base/axis_chart/axis_chart_data.dart

@@ -17,12 +17,16 @@ class AxisChartData extends BaseChartData {
   /// clip the chart to the border (prevent draw outside the border)
   bool clipToBorder;
 
+  /// A background color which is drawn behind th chart.
+  Color backgroundColor;
+
   AxisChartData({
     this.gridData = const FlGridData(),
     FlBorderData borderData,
     this.minX, this.maxX,
     this.minY, this.maxY,
     this.clipToBorder = false,
+    this.backgroundColor,
   }) : super(borderData: borderData);
 }
 

lib/src/chart/base/axis_chart/axis_chart_painter.dart

@@ -12,14 +12,18 @@ abstract class AxisChartPainter<D extends AxisChartData> extends BaseChartPainte
   final D data;
 
   Paint gridPaint;
+  Paint backgroundPaint;
 
   AxisChartPainter(this.data) : super(data) {
     gridPaint = Paint()..style = PaintingStyle.fill;
+    backgroundPaint = Paint()..style = PaintingStyle.fill;
   }
 
   @override
   void paint(Canvas canvas, Size size) {
     super.paint(canvas, size);
+
+    drawBackground(canvas, size);
     drawGrid(canvas, size);
   }
 
@@ -76,6 +80,25 @@ abstract class AxisChartPainter<D extends AxisChartData> extends BaseChartPainte
     }
   }
 
+  /// This function draws a colored background behind the chart.
+  void drawBackground(Canvas canvas, Size viewSize) {
+    if (data.backgroundColor == null) {
+      return;
+    }
+
+    final Size usableViewSize = getChartUsableDrawSize(viewSize);
+    backgroundPaint.color = data.backgroundColor;
+    canvas.drawRect(
+      Rect.fromLTWH(
+        getLeftOffsetDrawSize(),
+        getTopOffsetDrawSize(),
+        usableViewSize.width,
+        usableViewSize.height,
+      ),
+      backgroundPaint,
+    );
+  }
+
   /// With this function we can convert our [FlSpot] x
   /// to the view base axis x .
   /// the view 0, 0 is on the top/left, but the spots is bottom/left

lib/src/chart/line_chart/line_chart_data.dart

@@ -23,10 +23,12 @@ class LineChartData extends AxisChartData {
     double minY,
     double maxY,
     bool clipToBorder = false,
+    Color backgroundColor,
   }) : super(
     gridData: gridData,
     borderData: borderData,
     clipToBorder: clipToBorder,
+    backgroundColor: backgroundColor,
   ) {
     initSuperMinMaxValues(minX, maxX, minY, maxY);
   }