I don't think you're going to get any.
The last bug thread on the chestplate was
https://www.project1999.com/forums/s...d.php?t=161840, which determined that it should be black ... back in 2013.
Evidently, some time since that thread, Nilbog decided it should be brown with a smiley face instead (on some races at least).
Presumably he found some in-era evidence (either a screenshot from back in the day, or a site that listed the fashion categories of items, like say a ShowEQ log) ... but it could just be him trolling us.
Either way, without a bug thread Nilbog is the only one who knows, and he's very unlikely to explain himself, because that's just not how he rolls.