I recently made a gem that sets up a basic ruby/gosu game with some helper classes. Mostly for my own use when prototyping games I often create new projects, so I thought I might as well share it.
Not sure what you are meaning to correct there, but I think that should be Gosu::Color.argb(a,r,g,b) or Gosu::Color.rgba(r,g,b,a) (#new is equivalent to #argb, not #rgba)