The un-dyeable parts of leather can be reinforced with materials

The un-dyeable areas on leather armor are meant to distinguish it between regular armor, but it usually ends up looking worse, and if not, still isn't useful. So at a smithing table, you should be able to combine a leather piece of armor with a material to replace what can't be colored. For example, replacing the knees of leather pants with diamond will make them the color of diamond, etc. The adding of a material will improve the leather armor rating by the lower tier than that material, and the durability the same as that material. If you add a gold ingot, it has the same armor rating as leather but double the durability. If you add an iron ingot, it has the same armor rating as chain, but with the durability of iron. If you add a diamond, it has the same armor rating as iron, but with the durability of diamond. Lastly, if you add a netherite ingot, it has the same armor rating as diamond, but the durability of netherite. However, it has NO knockback resistance or immunity to fire.