I was trying to achieve an overlapping line chart with filled colors by setting the alpha channel of the background colour to be 0.5 but it simply does not work.

The colours are yellow and grey and when they overlap it should be a sort of yellow-grey if that makes sense.

Here you can find some pieces of my code to create the dataset:

{
  type: type,
  data: data,
  order: order,
  borderColor: borderColor,
  fill: true,
  yAxisID: yAxisID,
  pointRadius: pointRadius,
  backgroundColor: !previousSeason ? 'rgba(253, 242, 178, 0.5)' : 'rgba(225, 225, 227, 0.5)',
  borderWidth: borderWidth,
}