This is how I build a colour comic in Photoshop.

Scan the original drawing.

I start by scanning a black-and-white drawing.

The drawing should be drawn with colouring in mind. Large dark areas are generally added during the colouring, so they should not be done as part of the black-and-white drawing.

The colouring style I describe here relies on using the ‘bucket’ tool to fill large areas; they can also be filled using brushes.