Just for fun, often each electrical company/contractor (sometimes depending on who works for the streetlights) usually chooses the color of a Photocell as a standard and will sometimes change overtime in many years.
For my area
Baltimore Gas and Electric: as from what I have seen, they most commonly today are using black photocells in most cases which almost all setups are 120 volts, but I was told they use blue for the higher voltage setup which I am not 100% sure. Before they started using black ones, they were grey, and before that Fisher Pierce made them with clear plastic with colored paint inside back in the 60s early 70s. And they were light blue in this case.
PEPCO: I am honestly not sure there seems to be too many variety of them in use, although I will have to look again since they did a recent group fixes since a lot of the mercs are now brighter and dayburners were turned off, but I am not sure if they replaced PCs for ones that did not dayburn. But I believe I saw some old PCs still in use.
The state of MD. Most cases I see they are blue..rich blue! But some installations I see are using Intermatic Inc PCs which has large voltage number around it.
Other areas are unknown for me for now.
How about your area/electrical company/city....