Are there color standards for US Transportation roads such as Interstate, County,, Interstate, local, private, state highway and other roads out there ?
In our office (we are a state agency) Federal Highways are Blue with slight black outline on each side of the line, State Highways are Red. Farm/Ranch to Market roads (small state highways) are Black or dark gray. County roads are slightly lighter gray. If a map is zoomed in close enough for city level roads they are kept a shade of gray as well. I cant say if this is a standard or not but its good map practice at least. Also I looked up your question and found this which may be of help http://www.quora.com/How-do-I-classify-colour-roads-and-boundary-features-in-arc-map