http://computergraphics.stackexchange.com/ is about algorithms. It is for computer graphics researchers and programmers.
http://graphicdesign.stackexchange.com/ is about design. For some reason there are lots of questions related to Illustrator, Photoshop and other 2D apps, but nobody asks questions related to 3D there. Also see this question: Is this a duplicate of Graphic Design?
This would be for users of 3D software. The closest to this is actually http://blender.stackexchange.com/, but that is too specific.
Possibly the name should be changed, see this: Naming (near) duplicate: 3D Computer Graphics and Computer Graphics