The level guide shows the colour from the forecast intervals which is blended with the series colour.
guide_level(title = waiver(), max_discrete = 5, ...)A character string or expression indicating a title of guide.
If NULL, the title is not shown. By default
(waiver()), the name of the scale object or the name
specified in labs() is used for the title.
The maximum number of levels to be shown using ggplot2::guide_legend().
If the number of levels exceeds this value, level shades are shown with ggplot2::guide_colourbar().
Further arguments passed onto either ggplot2::guide_colourbar() or ggplot2::guide_legend()