Change transparency of fillcolor

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]))