Cossacs people felt themselves different from peasants because peasants were enslaved in tsarist's Russia, and cossacks were not. And, cossacks demonstrated this difference in every way of life, including their clothes. First, they made their outfits as rich and fancy as it was possible. Second, they dressed boys in "inappropriately adult" style (from peasant's point of view). For instance, 10-12 year-old cossack boys wore costumes similar to peasants' 15-16 teens, and so on.
This shirt is
white, as it suppose to be for kids and pre-teens. However, the decoration is made of a golden trim, as for
One more point: cossacks could celebrate their difference, but spiritually they needed ancestors' protection as any "ordinary" people. That's why this shirt bears red protective trim ("fire line") at a hemline, sleeve cuts, and around a neck.
The whole style of the shirt is modest (as it has to be for kids). It has no lastovica (red armpit details), and it lacks any
details demonstrating wealth (lining, wide sides, etc.)
A chest's "shield" could be decorated not only with ritual embroidery, but also with a fancy trim.