Gentlemen, Not every ship has a yellow box. Unless I'm mistaken, it was to indicate the ship had separate engineering spaces with two complete sets of everything (parallel machinery), so if one engine room was disabled, the other could quickly separate itself and provide power for movement and all other needs (electricity, steam for cooking etc.) Not all ships with two funnels were so arranged. While there may have been multiple boiler rooms, the ships machinery (turbines, gearing etc.) may not have been separated. This was an older set up, but by no means unusual in WW2. Most all new warships were built this was however.
Obviously you need color ships charts to see this ... But to assume that everything with two stacks had parallel machinery would be a mistake.