White for clear? Really? Does it have anything about lunar for restricted speed?
Nope, only these three, and named Brit-wise as Clear, Caution and Danger. OTOH, they did have blue for cars not to be moved or hooked to.
There is a copy on the Internet Archive, btw:https://archive.org/details/standardcodeofam00amer
It seems that back then, good yellow glass plain did not exist, and the searchlight was still twenty-odd years in the future.http://mysite.du.edu/~jcalvert/railway/railamps.htm