For inspiration I think grafana does a good job here so its a reasonable idea to emulate it.
In particular on /admin/reports/consolidated_page_views?start_date=2019-01-09&end_date=2019-02-09 you can display the label names and have them clickable, when bold they show when non bold they do not show the series.
One extra bit of interesting fancy grafana has is that you can use control as well which lets you select 2 out of 4.
Eg:
Not saying we emulate this 1-1, but its an interesting and nicely established pattern.