From what I can tell, it looks like the same yellow that outlines the rest of the armor scratches.
I plan to use zinc chromate for it.
Hope this helps.
Actually the correct color is Polly scale Catwhiskers yellow, it is used on the knees and shoulder bells around the silver scratchs. That is the color RougeStudios has pointed out in his thread http://tdh.prop-planet.com/viewtopic.php?topic=6556&forum=2 as being the actuall color used and is what I used on mine.
The Zinc chromate is used on the green armor.
Lynn