Efficiency Layout Achievement not triggered

I’m trying to unlock Charcoal Black which requires the Efficiency Layout achievement. I edited a map to facilitate a compressed production area and managed to get 13.35 sq. meters per car per hour for one cycle by pausing exports until I had produced a backlog of cars. I then flushed them to hit that ratio.

Unfortunately the achievement did not pop so I’m guessing I don’t fully understand what needs to be done. Any suggestions?

Aside from Lime Green and Deep Blue, which will unlock in time of their own accord, this is the only color I haven’t been able to access. I don’t even care for the color but seeing that padlock in the design screen just bugs me.