The file chestplateCloth_overlay.png in minecraft.jar/textures/items appears to be incorrect. It has an empty alpha channel and the image itself is of an undyed brown leather tunic.
Is this maybe caused by the fact that in the old-style items.png the overlay is blank?
It appears to have no affect on the ingame look of the tunic.
I have attached chestplateCloth_overlay.png and also a version with full alpha, demonstrating that it is of the brown leather tunic.
Edit: On further experimentation, this seems to be caused by the unstitcher, and similar things happen with other texture packs, however I have not pinned down whether this is specific to leather armor overlays.