Just wanted to let somebody know, there seems to be a bug with part_color. It seems to ignore the 4th argument (alpha value). I can see from the code how this happens, as line 56 of part_color.cpp is:

pColorD(1.0f, PDLine, m_color1[0], m_color1[1], m_color1[2], m_color2[0], m_color2[1], m_color2[2]); 

which clearly doesn't make any reference to m_color1[3] or m_color2[3] (the alpha values passed into the object.

Apologies if this isn't the correct place to post this, but couldn't find anywhere better given the limited time I have.