GTIN exception and Variations

Hi Guys, I’ve sold a few branded products on Amazon but I’ve just received my first shipment of unbranded products (no barcode). There are 3 variations of the same item (different colours). Do I need to buy a barcode from gs1 for each variation if I have GTIN exemption for my brand or can I list them with nothing in the product ID box as I have the exemption?

Also could anyone recommend a good guide for creating a variation listing? All the ones I’ve seen/read are a bit out of date.

Thanks good people. Peace - DB.