您可以直接进入图表对象内部，进入选项并更改网格线的颜色：

const lightGridLineColor = 'black';
const darkGridLineColor = 'yellow'

const myBarChart = new Chart(ctx, config);

document.getElementById('chartChange').addEventListener('click', () => {
  const toDarkMode = myBarChart.options.scales.x.grid.color === lightGridLineColor;
  if (toDarkMode) {
    myBarChart.options.scales.x.grid.color = darkGridLineColor;
    myBarChart.options.scales.y.grid.color = darkGridLineColor
  } else {
    myBarChart.options.scales.x.grid.color = lightGridLineColor;
    myBarChart.options.scales.y.grid.color = lightGridLineColor
  }

  myBarChart.update();
})

活样品：
第一个