It's probably yellow for safety reasons to remind people to be cautious around them because the streetcar wires are live and they don't have any insulation on them as they are just bare wires.It's too bad they couldn't have matched the colour of the bridge instead of using bright yellow.
I love how they have installed that terracotta capital on the Bay upside down.
Not quite square peg round hole' but still quite the oversight. The downside-up capital also seems to be a different colour, a replica replacement..?
I wonder if it could be an intentional thing. Sometimes in architecture, there is a tradition of making a small mistake like that.