The Graphite time series query language supports time shifts, so you can compare one metric against itself but for a different time range.
For example in the graph above we show dashboards downloaded on grafana.com/dashboards grouped into 6 hour buckets. You can also see the series but last week so you can easily compare how the current values compare against the week before.
If you zoom out so the time range is bigger then the time shift you can see how the green line is mirrored in the faint time shifted series further along the graph.
To accomplish this visual look we need to use a series override.
The override sets a line fill and disables line width on the time shifted series. This creates the desired "shadow" effect for the time shifted data.