hi. Illustrator is a vector drawing app and therefore will need the artwork to be vector to fully utilise its functions. As the image is raster you will need to draw/"tell" illustrator what and where to colour. I think for what you are trying to achieve from what you have, photoshop will be easier to use.
Can you please show a screenshot and tell us if youare working with vector or raster artwork?
Apart from that: the live paint function might help you https://helpx.adobe.com/illustrator/using/live-paint-groups.html
Contrary to popular belief, Illustrator will not read your mind though. You still have to use the tools.