I drew an image in Illustrator and now I would like to fill it with color. I created a second layer and placed it under the line art.

However when I try to painting with the brush tool I get a really annoying  (international prohibition sign / no symbol).

*Why is that?*
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[![](https://i.stack.imgur.com/vn3tD.gif)](https://i.stack.imgur.com/vn3tD.gif)

[![layers panel](https://i.stack.imgur.com/27M7p.png)](https://i.stack.imgur.com/27M7p.png)