When users hover their mouse over series and points on the graph a highlight effect appears on the surface of the graph. You can use the dyHighlight function to customize how the highlighting appears.

In this example we specify a larger circle size for point highlighting as well as more decisively fade the non-highlighted series. We also request that the highlighting persist even after the mouse leaves the graph area.

lungDeaths <- cbind(ldeaths, mdeaths, fdeaths)
dygraph(lungDeaths, main = "Deaths from Lung Disease (UK)") %>%
  dyHighlight(highlightCircleSize = 5, 
              highlightSeriesBackgroundAlpha = 0.2,
              hideOnMouseOut = FALSE)

You can also set additional visual options for the highlighted series using highlightSeriesOpts. This argument takes a list of named series options to apply to just the currently highlighted series (see the dySeries function for the various options that can be set). Here we set the stroke width of highlighted series to 3:

dygraph(lungDeaths, main = "Deaths from Lung Disease (UK)") %>%
  dyHighlight(highlightSeriesOpts = list(strokeWidth = 3))
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