All of the plants bought these grease pencils, or paint daubers or whatever other sort of marking device they used by the case lot from the cheapest vendor. And when they went to general stores to req them out to use, if G.S. didn't have a particular colour, they'd use whatever was on hand.
I don't think in any of the chassis graphics books I've ever seen there's a callout for a torque I.D. mark to be a specific colour. Those marks are all a visual confirmation for a quality control check.
There's a slim possibility that the colour changed with the shift, or an even more remote chance the colour was specific to an individual operator. Inspection stamps are may have been specific to the inspector using them, but that's as close as you'd come to tying a specific mark to a specific individual.