I’m sure that you alraedy saw a lot of people on agar.io that have custom cell backgrounds like their countries flag.
Well, you can do this too. If you want to play agar.io with the US Flag, just chose “usa” (without quotation marks) when you enter in the game. This will autmatically put the flag of US on your agar.io cell. Check here the full list of agar.io available skins.
Also what do you think about the idea of creating custom skins for agar.io?
If you don’t know, agar.io allows you to create your own skin. There are a few rules that you need to follow to get your custom agario skin approved. You can read them here.