context_dependent_knob.dart

import 'package:flutter/material.dart';
import 'package:widgetbook/widgetbook.dart';

class ColorValue {
  ColorValue(this.name, this.selectorFn);

  final String name;
  final Color Function(BuildContext) selectorFn;
}

Widget build(BuildContext context) {
  final colorFn = context.knobs.options(
    label: 'color',
    options: [
      ColorValue(
        'primary',
        (context) => Theme.of(context).colorScheme.primary,
      ),
      ColorValue(
        'secondary',
        (context) => Theme.of(context).colorScheme.secondary,
      ),
    ],
    labelBuilder: (v) => v.name,
  );

  final color = colorFn.selectorFn(context);
  return Container(color: color);
}