Updating a chaco plot selected line color

I have a chaco plot object which stores several lineplots.  I have looked
through the Plot source and I am able to access the individual lineplots
using the name parameter.  For example, if I make a plot with 2 lines:

plots.plot( ('x', 'y'), name='plot1', color='green')
plots.plot(('x2','y2'), name='plot2', color='red')

Then I am able to access the lineplots individually with:

selected_lineplot=plots['plot1']

Everything is fine, but let's say I'd like to change the color of 'plot1'
to orange. I do the following:

plots['plot1'].color='orange'

The color trait is updated, I've checked, but the color on the plot is not
updated.  I've tried doing a request_redraw() on the whole plot and nothing
changes.  Any idea why there's no automatic update when I change the color
this way?

Thanks.