geom_line becomes invisible when color aesthetic applied

I am attempting to apply a gradient color scale to a line in a ggplot object. When I create the plotly chart, the plotted line is not visible. Hovering over the plot area shows the values of the variables if the cursor is where the line is located, even though the line is not visible.

If I do not apply a color aesthetic, the line is visible.

I have download the most recent plotly package from Github.

Here is some example code of the issue:

library(tidyverse)

df <- tibble(
x = rnorm(100, 7, 1),
y = rnorm(100, 4, 1),
z = rnorm(100, 5, 1))

plot <- ggplot(df) +
geom_line(aes(x, y, color = z),
lwd = 1.5) +
scale_color_gradient(low = "red",
high = "blue")

plot

plotly::plotly_build(plot)

ggplot:

Start by running the issue's R example with ggplot2, geom_line(), scale_color_gradient(), and plotly::plotly_build(plot), comparing it with the version without a color aesthetic. Trace the conversion from the colored ggplot line to the Plotly chart; done means the line is visible while retaining its gradient colors and hover values.