I am ordering class flags for the NOYC RC.

What flags are used to start J/30s across the country? Is there a standard color or is the class flag used?

Chesapeake Bay YRA assigns code flags to classes or fleets. J/30s became "D" 20+ years ago. The idea is that many different clubs run races and they all carry a full set of code flags. In practice with so many code flags used under the modern RRS, there are fewer left for use by classes. CBYRA is down to 3rd Substitute and will soon have to recycle some from dying (or dead) classes.

The local dinghy club SSA uses class logos on white flags.