当使用scale_color_gradientn时，ggplot2传奇条目从posixct变为整数

I'd like to make a path plot in ggplot2, with the path based on a timeseries, and a continuous color aesthetic to show this path. The legend should associate the color with timeseries. The legend is nice when the color aesthetic is defined in the original call to ggplot:I'd like to make a path plot in ggplot2, with t