An itemstack of Material.SPAWNER will always have a light purple item name. This happens both if you don't change the item name and if you manually rename it. Even if you add ChatColor.RESET in front of the displayname of the itemstack, it will still appear light purple. In 1.16.5 Spigot, the item name was the default white, which I believe is the correct color.

How to demo:

use the vanilla command: /minecraft:give @p minecraft:spawner and the item will have a light purple name. If the same command is used on a 1.16.5 server, it will have the correct white name.

 EDIT: Using ChatColor.RESET + "" + ChatColor.WHITE in front of the name does it make it appear correctly, but the bug with the default give command giving it a purple name is still there.