How do I change the Shulker GUI title in Minecraft plugin using Kotlin Maven

Apparently I'm making a plugin that make Shulker box works like a backpack. You can right click to open them on your main hand or even off-hand. I have all the function I needed but I want to change the title of the GUI appearing when I right clicked.

Here's the GUI!

As you can see there it showed "Shulker Box" and I want to change it (it would be awesome if we can use color code with "&" instead of section symbol)

Is there anyway I can change that title? I already have ProtocolLib latest version inside my project and this is my first time developing a GUI plugin like this.

Here is my kotlin maven code (I'm developing paper plugin):

package me.hoangxuanlam2007.baloshulker

import org.bukkit.Material
import org.bukkit.block.ShulkerBox
import org.bukkit.command.Command
import org.bukkit.command.CommandSender
import org.bukkit.entity.Player
import org.bukkit.event.EventHandler
import org.bukkit.event.Listener
import org.bukkit.event.block.Action
import org.bukkit.event.inventory.InventoryCloseEvent
import org.bukkit.event.player.PlayerInteractEvent
import org.bukkit.inventory.EquipmentSlot
import org.bukkit.inventory.ItemStack
import org.bukkit.inventory.meta.BlockStateMeta
import org.bukkit.plugin.java.JavaPlugin

class BaloShulker : JavaPlugin(), Listener {

private val openedShulkers = HashMap<Player, ItemStack>()

    override fun onEnable() {
        // Register the event listener
        server.pluginManager.registerEvents(this, this)

        // Log a message to the console when the plugin is enabled
        logger.info("BaloShulker plugin enabled!")
    }

    override fun onDisable() {
        // Log a message to the console when the plugin is disabled
        logger.info("BaloShulker plugin disabled!")
    }

    @EventHandler
    fun onPlayerInteract(event: PlayerInteractEvent) {
        val player = event.player
        val action = event.action
        val hand = event.hand
        val item = if (hand == EquipmentSlot.HAND) player.inventory.itemInMainHand else player.inventory.itemInOffHand

        // Check if the player is holding a shulker box in the hand and right-clicked in the air
        if (isShulkerBox(item) && action == Action.RIGHT_CLICK_AIR) {
            event.isCancelled = true

            // Open the shulker box
            openShulkerBox(player, item)
        }
    }

    private fun isShulkerBox(item: ItemStack): Boolean {
        return item.type == Material.SHULKER_BOX || item.type.name.endsWith("_SHULKER_BOX")
    }

    private fun openShulkerBox(player: Player, shulkerBoxItem: ItemStack) {
        val shulkerBoxMeta = shulkerBoxItem.itemMeta as? BlockStateMeta

        if (shulkerBoxMeta != null && shulkerBoxMeta.blockState is ShulkerBox) {
            val shulkerBox = shulkerBoxMeta.blockState as ShulkerBox
            player.openInventory(shulkerBox.inventory)
            openedShulkers[player] = shulkerBoxItem
        }
    }

    @EventHandler
    fun onInventoryClose(event: InventoryCloseEvent) {
        val player = event.player as? Player

        // Check if the player has a shulker that was previously opened
        if (player != null && openedShulkers.containsKey(player)) {
            val shulkerBoxItem = openedShulkers[player]
            if (shulkerBoxItem != null) {
                saveShulkerContents(shulkerBoxItem, event.inventory.contents.filterNotNull().toTypedArray())
            }

            openedShulkers.remove(player)
        }
    }

    override fun onCommand(sender: CommandSender, command: Command, label: String, args: Array<out String>): Boolean {
        if (command.name.equals("bs", ignoreCase = true) && args.isNotEmpty() && args[0].equals("open", ignoreCase = true)) {
            if (sender is Player) {
                // Check if the player has the permission to open shulker boxes
                if (sender.hasPermission("baloshulker.use")) {
                    val itemInMainHand = sender.inventory.itemInMainHand
                    val itemInOffHand = sender.inventory.itemInOffHand

                    // Check if the player is holding a shulker box in either hand
                    if (isShulkerBox(itemInMainHand)) {
                        openShulkerBox(sender, itemInMainHand)
                    } else if (isShulkerBox(itemInOffHand)) {
                        openShulkerBox(sender, itemInOffHand)
                    } else {
                        sender.sendMessage("You are not holding a shulker box!")
                    }
                } else {
                    sender.sendMessage("You don't have permission to use this command!")
                }
            } else {
                sender.sendMessage("Only players can use this command!")
            }
            return true
        }
        return false
    }

    private fun saveShulkerContents(shulkerItem: ItemStack, contents: Array<ItemStack>) {
        val shulkerBoxMeta = shulkerItem.itemMeta as? BlockStateMeta

        if (shulkerBoxMeta != null && shulkerBoxMeta.blockState is ShulkerBox) {
            val shulkerBox = shulkerBoxMeta.blockState as ShulkerBox
            shulkerBox.inventory.contents = contents
            shulkerBox.update()
            shulkerBoxMeta.blockState = shulkerBox
            shulkerItem.itemMeta = shulkerBoxMeta
        }
    }
}

Solution

Inventories tied to block states can not have their names changed trough the BukkitAPI directly. Titles of these inventories are tied to the display name which is set in their meta. You either have to create your own GUI with your customized name, or just rename the shulker box through their meta.

val shulkerBoxMeta = shulkerItem.itemMeta as? BlockStateMeta
shulkerBoxMeta.displayName(
    ChatColor.translateAlternateColorCodes('&', "&7My cool gray shulker!")
);