Nevernought (http://www.furaffinity.net/view/20587667/ ), Zepto's old teacher, was one of the finest anti-mages around. Like any wizard, he gave grand industrious names to each of his techniques, such as this one. A sphere of anti-magic, perfectly suited to get rid of curses and enchantments.

Why is Zepto a blue copper dragon? As many are aware, different dragons have different abilities, and shapeshifting is hard. Shapeshifting a squirrel into a mouse is already a complex affair, but turning a dragon into another dragon is the very apex of the technique. It was this that was attempted on Zepto, by an unnamed wizard, but luckily this bastard wasn't very talented and only managed to change the colours & horn shape. Less of a transformation, more of a 'permanent recolouring'.

Because Zepto deals a lot with anti-magic himself, he prefers to keep the blue as an anti-magic indicator, warning him of other nearby countermages.