I'm trying to change the default color of a fillcolor in Plotly to another transparent one, but when I change the fillcolor it is not transparent anymore.

trace = (go.Scatter(x=[30,45],y=[3000,3000],
                fill='tozeroy', 
#                     fillcolor='green',
#                     fillcolor='rgb(26,150,65,0.5)',
#                     fillcolor=dict(color='rgb(26,150,65,0.5)'),
#              fillcolor=dict(marker=dict(color='rgb(26,150,65,0.5)')),
                opacity=0.1,
                showlegend=False,
                hoverinfo='none',
                mode='none'))
py.offline.iplot(go.Figure(data=[trace]))

This default call results in the following:

and when I use fillcolor='green' it results in this nontransparent color:

The commented code results in the default case again.

You would need to use rgba to specify the alpha channel as well, rgb ignores the transparency.

import plotly
trace = plotly.graph_objs.Scatter(x=[30,45],y=[3000,3000],
                                  fill='tozeroy', 
                                  fillcolor='rgba(26,150,65,0.5)',
                                  mode='none')
plotly.offline.iplot(plotly.graph_objs.Figure(data=[trace]))