This question is related to question about what is UX but goes more into details.
Comments on this question (Has this design got a name? (Overflow illustration out of web card)) got me thinking whether we have any guidelines on what visual design questions are considered on-topic. Visual design is a big part of user experience but which questions are better to be asked at Graphic Design SE? I know GD.SE and UX.SE do a lot of bleeding but how much visual design is too much for UX.SE?
Differences between UX.SE and GD.SE have been discussed for example in this answer to UI merging with GraphicDesign.