NeumorphicToggle doesn't support transparent foreground

[robnorr]

I'm using a NeumorphicToggle to control tabs. It looks great, however when I set color of the thumb's style to Colors.transparent, I get a pale blue foreground toggle element, not a transparent one. The background element works perfectly.

Setting the thumb style color to anything else works fine (e.g. Colors.red):

NeumorphicToggle(
  style: NeumorphicToggleStyle(
    backgroundColor: Colors.transparent,
  ),
  height: 50,
  selectedIndex: _tabController.index,
  displayForegroundOnlyIfSelected: true,
  children: [
    ToggleElement(
      background: const Center(
          child: Text(
        "Tab 1",
        style: TextStyle(fontWeight: FontWeight.w500),
      )),
      foreground: const Center(
          child: Text(
        "Tab 1",
        style: TextStyle(fontWeight: FontWeight.w700),
      )),
    ),
    ToggleElement(
      background: const Center(
          child: Text(
        "Tab 2",
        style: TextStyle(fontWeight: FontWeight.w500),
      )),
      foreground: const Center(
          child: Text(
        "Tab 2",
        style: TextStyle(fontWeight: FontWeight.w700),
      )),
    ),
  ],
  thumb: Neumorphic(
    style: NeumorphicStyle(
        boxShape: NeumorphicBoxShape.roundRect(
          BorderRadius.all(Radius.circular(12)),
        ),
        color: Colors.transparent),
  ),
  onChanged: (value) {
    setState(() {
      _tabController.animateTo(value);
    });
  },
)

platform is MacOs