YouTube's highest profile ad placement has a new home and a new look.

This week YouTube extended its homepage-takeover ad to the Google-owned video service's mobile apps for the first time. And to mark the occasion, YouTube has updated the ad's look on smartphones and tablets with a so-called native aesthetic.

The mobile masthead ad swaps out the traditional horizontal banner image for a new design that appears akin to a regular video listing, aside from the yellow tag marking it an ad. BTIG analyst Richard Greenfield first spotted the new format.

"We created a video masthead unit that makes it easier for advertisers to run homepage takeovers on YouTube across devices," said a YouTube spokesperson who confirmed the redesign marks the first time the mobile masthead ad appears in YouTube's mobile apps.

It's unclear how the expanded reach will impact the takeover ad's price. Roughly 40% of YouTube's views occur on phones and tablets, but a spokesperson declined to say what share of those views take place within the mobile apps or comment on pricing. Google's chief business officer Nikesh Arora said in July that YouTube mobile-ad sales had jumped by 300% between January and June of this year.

YouTube's homepage ads are Google's most prominent display unit, and key to building its display ad business, which leads Facebook and Yahoo in the U.S., according to eMarketer.

The new format is said to be officially rolled out and available to advertisers, though Chevrolet's takeover campaign on Tuesday appears to be using the old design and doesn't show up in YouTube's iPhone or iPad apps.

The thinking behind the new format is that advertisers need only submit the video they'd like to promote, and YouTube formats how the ad should look on desktop computers, tablets and smartphones. The ad functions the same as the old format, as Mr. Greenfield demonstrated in a video he recorded.