1. To change the color of a line in a line chart so that it changes halfway through, you can follow these steps:
2. Select the line that you want to change the color of by clicking on it once.
3. Right-click on the line and select "Format Data Series" from the drop-down menu.
4. In the "Format Data Series" pane that appears on the right side of the screen, click on the "Fill & Line" tab.
5. Under the "Line" section, click on the "Solid line" option.
6. Click on the "Color" drop-down menu and select the color that you want the line to be for the first half of the chart.
7. Under the "Gradient line" section, click on the "Type" drop-down menu and select "Linear".
8. Click on the "Angle" drop-down menu and select "90 degrees".
9. Click on the "Stop position" drop-down menu and select "50%". This will create a gradient effect that changes the color of the line halfway through the chart.
10. Click on the "Add" button to add a new color stop.
11. Select the new color stop and choose the color that you want the line to be for the second half of the chart.
12. Adjust the "Stop position" as needed to ensure that the color change occurs at the desired point on the chart.
13. Click "Close" to apply the changes to the line chart.

By following these steps, you can create a line chart with a line that changes color halfway through.