Tell me, does that texture, the texture that was, according to the Minecraft Wiki's Horse Armor Change Log, supposed to have been released on 1.13 Pre-Release 2, look like the texture from the screenshot of my dummy horse wearing the current Iron Horse Armor texture? I think not. NO MODS, NO TEXTURE PACKS, NO RESOURCE PACKS, NO NOTHING!!
[media]!
[media]!! the last change was supposed to be for 1.13 Pre-Release 2, from June 15th 2018, and it never happened. You said it was fixed, it wasn't. There, enjoy. And I'll keep posting this exact same bug report, every day if I must, until the issue is fixed.
Do not duplicate your own tickets.