Anti-aliased black lines?

[Kurt Akeley]

I'm not an expert on the PI, but I understand that it uses only half of
the color indexes in the 16-index ramp when it generates antialiased
lines.  Probably the half that is used is either 0,2,4,6,8,10,12,14 or
1,3,5,7,9,11,13,15, but I don't know.  In any event, this would only
partially explain your observation.

-- kurt

p.s. I mailed this response to you some time ago, but the mail bounced.