secondaryActiveColor property Null safety
The color to use for the portion of the slider track between the thumb and the Slider.secondaryTrackValue.
Defaults to the SliderThemeData.secondaryActiveTrackColor of the current SliderTheme.
If that is also null, defaults to ColorScheme.primary with an opacity of 0.54.
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? secondaryActiveColor;