Take one old plain white shirt.
Grab a heart paper punch... Or whatever shape you want on your collar! Spots? Diamonds? Go for it! Punch shapes out of stickers/labels. Mine were saved from another project which is why they are coloured. They were just plain printer labels.
Remove the backing of the stickers and place the outlines on the collar, arranged however you want.
Paint fabric paint onto the shapes, carefully.
Allow to dry, remove stickers and seal collar with an iron or as per instructions on your chosen fabric paint.
Wash and dry your shirt and hey presto! Quick upcycle done! I normally don't like wearing shirts but this is a cutie now. I'm thinking about another collar project next... Sewing pearls to the collar tips of a denim shirt.