I remember the Haskell community actually sat down and had a community discussion about laying down design guidelines for the entire Haskell ecosystem (all packages should use so and so a color scheme, this is our logo, this is our font, etc.). I find Haskell sites almost always aesthetically pleasing, and it was probably due to conscious decision by the community to establish design standards.

I think OSS in general could benefit from giving a designer such broad-brush authority over an entire ecosystem.