There is a legal size req for our plates, regulations about the colour of it, and the size and font of the numbers must be the one they say.
Really its all about speed cameras imo, they dont you flying past with plates it wont pick up so the enforce these laws.
The black plates look ok so im not fussed using them for as long as i get away with it.
The smaller black ones look like this, a lot cooler looking,