Lineart Tutorial
An annoying problem I have encountered when colouring pictures is that white
background.

Duplicate the background layer.

Delete the original background layer.
NEXT click on the 'Channels' tab next 'Layers'.

You will get something
like this.

Now hit 'Delete.

One way to fix the transparency of the lines themselves would be by locking
the
transparency
and
going
over
the
lineart
with
a
large
brush...
And the other would be by simply duplicating your lineart layer and merging the
layers together.

Presto. Lineart ready to colour.