paint tool isn't working

Hello!

Since English isn’t my first language, I’m attaching an image to make my question as clear as possible.

I want to paint on drawings I made on toon boom For coloring, I wanted to use paint tool to make coloring process faster and
also wanted to separate the line and the color. So I made line work on ‘U’ layer, and was going to paint on ‘C’ layer so that I can separate those two later on.

but it seems impossible to use paint tool on C layer of a shot that I did drawing on U layer? I’m only able to color with brush tools.

Do I only get to paint on the same layer as drawing layer? Then what would be the point of separating layers into 4 different types as O,L,C.U?
Or if I ever want to paint on the C layer, using brush tool and painting page by page would be the only option ?

Thank you.

You need to create an art line of those brush lines. Select them all and, in the tool properties of the selection tool, you have the action “create colour art”. It creates invisible strokes on the colour layer and then you can paint in it with the bucket.

Thanks for helping us noobs!