Blue Flame Release: Aōdama

Overview
Blue Flame Release: Aōdama is a technique that infuses blue flames within the Rasengan. This gives it this blue aura effect as if there were a blue light source inside of the Rasengan. When the Rasengan hits a target a small burst of blue flames forms around the Rasengan to finish off the target.

Creation
The Blue Flame Release: Aōdama was created on accident while Aoi Kenju was learning the Rasengan. He added blue flame release into the Rasengan unintentionally. He actually didn't know until months later when he used this technique on someone in the chunin exams. Aoi struck his opponent with this technique that almost killed them if it wasn't for Aoi controlling the size of his Rasengan.

Reference
Rasengan