About all I can say is ... wow! Transit signal indications not even consistent within the same company! Thought a small comment at the bottom suggests that the "Green Line" signaling is probably what's used on the other light rail lines now. LA's Red/Purple lines are all subway and shouldn't need much wayside signaling - it's all cab signals or automatic controls or both.

I suspect there's a difference in some systems regarding what the signals are used for, too. In Sacramento, my observation has been that the signals on newer parts of private r/w primarily indicate whether all the crossing gates are down to the next station when a train is ready to leave a stop - yellow if the first few are down, green if they all are (or perhaps if the progression timing is working correctly for longer runs between stops). Though in the older sections of the lines there are separate signals at stops for the crossing gates. With trains usually 15 minutes apart and little single-track work any more, the ABS or CTC function is more of a fallback than regularly used in most of the system. The link to LAMTA indications suggests that at least some signals are controlled by a dispatcher or a system similar to ABS.