Actually, SVG can use "classes" just like CSS, so it could be easily recolored in SVG too.
I suppose the main thing you'd need is a data source mapping the stations and lines, then build it in whatever technology from that. The information page doesn't mention where the data came from, so I imagine it was manually created. I don't think TfL would be too willing to provide that data either, judging by the comments regarding licensing etc. in this thread.
With this CSS map a user could customise the colour/pattern of just a couple of problem lines (I could already in Firebug, but it would be great if there was a control panel to fiddle these things and then provide print/save links). Just an idea!