A little like that, after it's been rubbed off.
At first, it's a bit like when you put the tip of a felt tipped pen on wet kitchen paper (sorry, best example I can give ???) and it spreads out. After I rubbed it of the potato looks ok, except if it's got into any crevices etc. Also, it seems only to effect the immediate area (though, that may be because it's not had the chance to infect further, not sure).
Thanks
Lee