Update/Visit Sprite on Render Texture From Another Thread

I my coloring app which use flood fill make the app unresponsive and lots of ANR being reported on play dashboard. I Have tried to use std thread but when i visit any any sprite /Image on it in a separate thread the texture is rendered as black but same same code is working if I execute is on cocos/main thread.

You can’t update any Cocos object from anything but the main thread.