I've seen lots of steel airframe parts painted in zinc chromate.
There are two types of zinc, a darker green seen on the chassis in the pics, and a lighter one that's commonly seen painted on ally airframe parts/structures.
The darker shade always seems to be painted on steel parts/sub structures like engine mounts or trussed steel airframes and I can't recall why, A&P school was so long a go!
Most likely they just picked up a rattle can and went to it.
The majority of car guys just figure if it's off an airplane it has to be good.