Parcoords line opacity, rgba color not working

The documentation specifies that the parcoords' line argument color can be a an rgba string. This doesn't work though and the lines remain a solid color as if using only the rgb part.

import plotly.express as px
import plotly.graph_objects as go

iris = px.data.iris()

fig = go.Figure(
 data=go.Parcoords(
    line_color="rgba(100,00,0,0.1)",
    dimensions=list([
        dict(label='sepal_length', values=iris.sepal_length),
        dict(label='sepal_width', values=iris.sepal_width),
        dict(tickvals=[1, 2, 3],
             label='species', values=iris.species_id,
             ticktext=iris.species_id.unique()),
    ]))
)

fig.write_html('parallel.html', auto_open=True)