How do I change color of data plot line

So a) yes it is possible to selectively color segments of a line different colors. You can use VBA or manually you can click on the line (entire series is selected) then click on a it again and the nearest data point is selected. Right click and select 'Format data point'. Then click the paint bucket and under the 'Line' section change the color. You can then repeat for every data point/line segment you want to change. You can also use CTRL-arrow key to move point to point on the line.
That said, that is a lot of work and @Rine_van_Eekelen method is much easier. 1 tip to make it easier is that you can keep you existing columns and just copy the data UP TO 06-30 into a new column. Then add that new column as a new line on the graph and it can sit 'on top' of the existing line. In this way you can maintain the full column of data you have.

here is the previous example updated this way:

So the second column "Orig data" just needs to be copied once since it won't change.

I also show how I could change an individual segment inside the blue line to green.