In other words, that's not a paint job you're seeing there.
The walls are being sandblasted by workers during the overnight shift, according to BART spokeswoman Alicia Trost. Crews began washing the platform level track walls at Embarcadero in 2013, finishing one side of the tracks after 12 months. They've now started on the other side.
The walls are made of white terrazzo, and the discoloration you see is the result of brake dust that builds up from decades of BART and Muni trains rolling through the station.
"Because Embarcadero is the first station out of the Trans Bay Tube," Trost said in an email. "The walls collect all the subway grime and train brake dust that blows out from the tube."
The brake dust is safe and contains nothing toxic, according to Trost. It is organic material and there are no traces of lead or asbestos.
Dust collection is nothing new to Embarcadero station. Earlier this year the large rope-sculpture "Legs" by Barbara Shawcroft was removed after decades of being on display. The once orange installation grew so sooty it was barely recognizable.
The Embarcadero BART station is getting a thorough cleaning this week, which is great until you see just how disgusting they were all along.