Are you sure? I attached a picture of the area that you mean, I think. The 'greenish' yellow, is yellow paint, but put on very light so the brown background shines through, making it a bit 'greenish'.
The other yellow in the image is also yellow, but has a pink background, making it a bit off. The same effect happens at the barrels and the upper part of ckong's mouth,
Anyway, both colors are hard to pick from an image, so I leave it at one yellow color. I'm pretty sure that the workers at the Zaccaria plant did also only use one yellow color