sekelsta.horse_colors.client.HorseGui should extend net.minecraft.client.gui.screen.inventory.HorseInventoryScreen. Then you can override the functions with the ones that you already coded. It will improve the compatibility with other mods that will still be able to use HorseInventoryScreen while your mod is loaded.

Context: My horse statistics mod is using the HorseInventoryScreen class to get the data. But when your mod is loaded, the horse screen is replaced by yours which breaks some features of my mod.

Those private fields are a pain, but alright. I'll try it.

This is released as of yesterday (version 1.5.0)

Thanks for your work!