What kind of background did you use for your adsense site to gain the most CTR?

Don't worry about it. You should worry about your job. Your job is not to make your ads relevant to other countries. This is Adsense's job. Exactly like your job is not to do link building to try to manipulate search results, it is google's job to rank sites and present users with the most relevant results.
So your job is to produce relevant content on your site, the rest will follow. As long as you don't understand this, you're wasting your time in all areas.

 

Oh I see, so if ads is irrelevant its ok?

 

Yes it's ok, for some visitors they will be irrelevant, for some visitors they will be relevant. Also depends on the country of the visitor, since I'm in thailand there is not much advertiser competition to display their ads in thailand, but visitors from US will have more chances to see ads about acne than me.
And also there is the ads which show to me because I've been on their websites before, like agoda and paypal, that's pretty stupid since I can't forget Agoda because I use it too book my hotels, always, and paypal, well I have an account since 2001 so why are they displaying a paypal ad to me, that's stupid
The last one in arabic I have no idea since I don't speak arabic, they could have put an ad written in thai, I don't speak thai but at least it would have made a little sense since I live there.

 

Your post totally makes sense to me, as google adsense is a contextual tool that changes according to user cookies and the content of the page.

 

i use plain background... it works good hahahaaaa

 

Plain background really work?? hrm??