It might be smooth() activated by default in some modes / versions.
2 pixels gray sounds like anti-aliasing.

> It might be smooth() activated by default in some modes / versions.

Nothing.
I'm using noSmooth() and with 1.5.1 and OPENGL mode, I can't draw a 1 pixel, black line. It always draws a 2 pixel and gray line.
With 2.0 (windows 64 bits) and P3D mode, the same. I can't draw a 1 pixel and black line.
It seems a problem with the OPENGL and my software (Windows 7, 64 bits) or my hard (Nvidia GeForce GTX 560).

curious, curious...

OpenGL has smoothing enabled all the time, regardless of whether you want it to be. And, in 2.0, all 3D renderers are OpenGL-based. I think that explains all of the issues that you have.

nothing to do.. it's a video card problem (my Nvidia GeForce GTX 560).

The wikipedia says about this problem:

"It has been reported by users as well as developers [13] [14] [15] [16] [17] [18] [19] [20] that nVidia 400-series cards have severe performance problems with 3D content-creation applications such as Autodesk Maya and 3ds Max, Blender, Rhinoceros 3D—as well as some OpenGL games—to the extent that video cards two generations older routinely outperform 400-series in such applications and games. The problem, which affects any OpenGL application using textures, involves accessing framebuffer contents or storing data on the GPU. So far, one customer using an OpenGL based application got a response from nVidia support indicating that the behavior is expected in the GeForce 400 line of cards, and no software update will help improving the performance of the hardware.[21]. The problem can be worked around with a hack by using a CUDA memory copy to access the buffer object."

and the 500 series is the same architecture as the 400 series...