The IItemColorSupplier function can be used to provide the Color Object to be used for whatever.

It might be required for you to import the package if you encounter any issues, so better be safe than sorry and add the import.
import mods.contenttweaker.IItemColorSupplier;

The IItemColorSupplier Function is a function with following parameters.

• IItemStack itemStack → the item whose color is being requested.
• int tintIndex → the tint index, use that however you like. The function needs to return an Color Object.