What picture app is it people use on instagram/twitter ?

[Omar]

I mean the pictures with the color effect in the background. I tried pics stitch , pics art, snap seed, etc

[Abbie Binion]

There is Pixlr Express, IPiccy, all that I know of.
But there is also websites like, Pixect, IPiccy, Pixlr, WebcamToy.
Hope I helped!
Btw, IPiccy is REALLY great if you want to get deep into it, like changing eye colors, aribrushing faces, and even changing your hair color!