I write in this format, the color of the nickname remains white:

{
"key.showcaseitem.showcaseitem": "Шифтануть предмет",
"showcaseitem.misc.shared_item": "§8%s§f Демонстрирует предмет:§6 "
}

Then just switch to the 1.19.2 branch:

It's not possible like that. You will have to change the code here:

My Minecraft version is 1.19.2, when building from the sources available here, version showcaseitem-1.21-1.0.0 comes out, the mod does not work in the game after building (the build is successful). Are the available sources relevant for version 1.19.2?

Thanks

It's not possible like that. You will have to change the code here:

Showcase-Item/src/main/java/com/ultramega/showcaseitem/ShowcaseItemFeature.java

Line 104 in 7e34f5f

MutableComponent comp = Component.translatable("showcaseitem.misc.shared_item", player.getName());

and write comp.setStyle(comp.getStyle().withColor(FastColor.ARGB32.color(r, g, b)))