title: Flutter RawMaterialButton won't get transparent
body: <p>I'm using this simple <code>CircularButtonWithIcon</code>. The one problem is that it won't respect transparency when no color is setted.</p>
  <pre><code>class CircularButtonWithIcon extends StatefulWidget {
    CircularButtonWithIcon({
      Key key,
      @required this.onPress,
      this.padding,
      this.border,
      this.active = false,
      this.marginRight,
      this.marginLeft,
      this.icon,
      this.color,
      this.activeColor,
      this.text,
      this.splashColor,
      this.image,
      this.hasState,
      this.borderColor,
    }) : super(key: key);
    final double padding;
    final double border;
    final double marginRight;
    final double marginLeft;
    final Icon icon;
    final Image image;
    final Color color;
    final Color activeColor;
    final Color borderColor;
    final Widget text;
    final Color splashColor;
    final Function onPress;
    final bool active;
    final bool hasState;
  
    @override
    _CircularButtonWithIconState createState() =&gt; _CircularButtonWithIconState();
  }
  
  class _CircularButtonWithIconState extends State&lt;CircularButtonWithIcon&gt; {
    bool active;
  
    @override
    void initState() {
      super.initState();
      active = widget.active;
    }
  
    @override
    Widget build(BuildContext context) {
      return FittedBox(
        child: Container(
          margin: EdgeInsets.only(left: widget.marginLeft ?? 0, right: widget.marginRight ?? 0),
          child: RawMaterialButton(
            onPressed: () {
              setState(() {
                active = !active;    // don't use widget.active
              });
              if (widget.onPress != null) widget.onPress();
            },
            fillColor: active
                ? widget.activeColor ?? widget.color ?? Colors.transparent
                : widget.color ?? Colors.transparent,
            splashColor: widget.splashColor ?? Colors.grey,
            child: widget.text != null
                ? Container(
              child: widget.text,
            )
                : widget.image ?? widget.icon,
            //padding: EdgeInsets.all(15.0),
            padding: widget.padding != null ? EdgeInsets.all(widget.padding) : EdgeInsets.all(15.0),
            shape: CircleBorder(
              side: BorderSide(
                  width: widget.border ?? 2.0,
                  style: BorderStyle.solid,
                  color: widget.borderColor ?? Colors.grey),
            ),
          ),
        ),
      );
    }
  }
  </code></pre>
  <p>Take a look at:</p>
  <pre><code>        fillColor: active
                    ? widget.activeColor ?? widget.color ?? Colors.transparent
                    : widget.color ?? Colors.transparent,
  </code></pre>
  <p>When no color is seted, it should be transparent.</p>
  <p>I did this:</p>
  <pre><code>                  CircularButtonWithIcon(
                        padding: 10,
                        border: 3,
                        onPress: () =&gt; {},
                        icon: Icon(Icons.remove,
                            color: Color.green,
                            size: 60))
  </code></pre>
  <p>and it's getting a color background instead of merging:</p>
  <p><a href="https://i.stack.imgur.com/gngxr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gngxr.png" alt="enter image description here" /></a></p>
  <p>however it looks like it's just the background but darker. Is it possible that the button is adding a shadow on top of the background color? How can I remove it? I looked at <a href="https://api.flutter.dev/flutter/material/RawMaterialButton-class.html" rel="nofollow noreferrer">https://api.flutter.dev/flutter/material/RawMaterialButton-class.html</a> and couldn't find anything related to shadow effects on the button</p>