inactiveColor property Null safety
The color for the inactive portion of the slider track.
The "inactive" side of the slider is the side between the thumb and the maximum value.
If null, SliderThemeData.inactiveTrackColor of the ambient SliderTheme is used. If that is null and ThemeData.useMaterial3 is true, ColorScheme.surfaceVariant will be used, otherwise ColorScheme.primary with an opacity of 0.24 will be used.
Using a SliderTheme gives much more fine-grained control over the appearance of various components of the slider.
Ignored if this slider is created with Slider.adaptive.
final Color? inactiveColor;