I want the error band from VisulaizeError() to be transparent, but I was not able to find the proper option for this. I have seen that for histograms there is a SetFillColorAlpha(), but that did not work in the plotOn() function and I have also not found a FillStyle() that is properly transparent.
The transparency is available on all platforms when the flag OpenGL.CanvasPreferGL is set to 1 in $ROOTSYS/etc/system.rootrc , or on Mac with the Cocoa backend. On the file output it is visible with PDF, PNG, Gif, JPEG, SVG, TeX … but not PostScript.