Corr.show() draws prange in same color as error bars.

[EhDings]

I was puzzled when I saw that a correlator had a large error in a plot from Corr.show() when print() gave me a small value.
It turns out, the markers for prange are identical to the error bars.
Here, in

        if self.prange:
            ax1.axvline(self.prange[0], 0, 1, ls='-', marker=',')
            ax1.axvline(self.prange[1], 0, 1, ls='-', marker=',')

it would be helpful, if color=... and maybe zorder were defined for axvline.
Nevertheless, I really like the convenience of the Corr class!
Thank you :)

[fjosw]

Hi @EhDings, thanks for opening this issue. We could maybe default the color of the plateau range indicator to black?! Including zorder also sounds like a good idea. Feel free to open a pull request with these changes if you want or I can also take care of this later.