"A colorful sleeve with magnets on it" describes the barebones case that Apple makes for pretty much every one of its products. But for some reason it didn't think to make one for the Pencil, so another company did.
Since late last year, Moxiware has been selling what it simply calls the Apple Pencil Magnet. It's a simple tube that you slip the Pencil stylus into that offers a bit of extra grip. But more importantly, it puts a long magnet along one side of the Pencil, which allows it to stick to the iPad, which has magnets embedded along two of its sides.
It's a simple and clever solution to the problem of having nowhere to store Apple's stylus when you're done with it. Is it the perfect solution? Definitely not, but remember that the Pencil charges by sticking out of the iPad's Lightning port, so we're talking about an imperfect device here.
Moxiware offers the Pencil sleeve in a handful of bright colors, all of which make the Pencil look a bit more fun than its current Jony Ive-approved white and silver. It's currently on sale for $16.95.