Apple will be releasing its own clear case for the iPhone XR.
This was found by Twitter user ivanincanada, who posted a screenshot of the Canadian press release for the iPhone XR from Apple's Newsroom. This mention of the clear case is only only the Newsroom post in some countries, like Canada for example.
Images of the case have also been leaked, showing a blue iPhone XR in a clear silicon case with a cutout for the single camera and flash (vertical). It seems Apple is going to be keeping it simple, and this will be the first ever plastic case it has released.
A leather or other silicon case would just hide the new colours, too.
It's probably going to be released after October 19th, when pre-orders start for the iPhone XR, which is available in Product(RED), black, white, yellow, blue and coral. The case will cost $55 CAD, around $40 in the US and probably about £32 in the UK.
You can read the press release on Apple's Canadian website (apple.com/ca) by clicking here and scrolling to the bottom of the page.
Author's Opinion: The case looks very simple, and nice, but at a price of £32 ($55), it's quite ridiculous. You can get very similar ones from third-party case manufacturers for less than £10.