I'm coming at this from a slightly different angle. You can interactively highlight different lines by setting up a slider in the live editor as per the demo I've attached. With this approach you can see all the other data while highlighting one line of interest at a time (in this case I just increase the linewidth and bring it to the front of the graph, though one could specify other line properties).
Advantages: You do not have to read down a list of 70 or more legend entries. You avoid any colour similarity issue, and furthermore, you ensure the line you want to assess is in the foreground; with 70 or more lines it is quite likely that many cover a large portion of the line you’re currently looking at.