I'm late chiming in on this post, but it is definitely a worthwhile post.
There is an organization that is dedicated to this. Check out the National CAD Standard at:
http://www.buildingsmartalliance.org/index.php/ncs/This is how we as a company are trying to structure our standards. While they do not have dedicated colors for each layer or item, they have guidelines to follow that will get everyone close to being on the same page with one another in terms of layers, title blocks, symbols, abbreviations, etc. That way if one company outsources work to another company, you would have a very good idea how the company operates.
Colors are a very good discussion though. We are on the piping side and the amount of services far outweigh the number of services the duct side has to deal with. They range from all the hydronic piping systems, steam/condensate systems, DWV systems, domestic water systems, medical gas systems, lab gas systems, industrial piping systems, and then the not your everyday systems. While there are 255 colors to choose from, a lot of them do not show up very well on a back background (or a white background), some of them do not plot well as previously mentioned, and some are just hard to look at depending on the screen clarity and brightness. Great topic!
