To be more precise a dark signal would be the most restictive indication the signal is capable of displaying. So an intermediate would be "stop and proceed" or "restricted proceed" on some railroads. An absolute signal would be "stop". Some signals never can display a red such as a distant signal. One could pass a dark distant signal at maximum speed prepared to stop at the next signal. The FRA requires railroads to test engineer reaction to dark signals on a regular basis.