If you are a Google AdSense user then this is something you might have faced initially and you know why this happens. So I thought all the upcoming and newbie AdSense users should know about this as well.
You got a blog, you applied for AdSense, you got approved and you eagerly created/placed the ads on your blog, but, it just shows a blank yellow box (or just blank) instead of ads. Scared? Don’t be. It’s just something temporary. That means Google is analyzing your blog (probably the text content) so that they can pick the right set of ads for your blog.
This might also occur if you enabled this option while creating ad units - “Collapse the ad unit, otherwise show color”. If Google doesn’t find any suitable ads for your blog, then this happens. So make sure you have good quality relevant content on your blog for proper ads.
Normally after creating an ad unit, it’ll take a few minutes for the ad to display, it depends on your site’s content and format. Let us know if you have any queries regarding this.