Problems creating an Alpha Channel in GIMP

[CmorEffect]

So I have hit a bit of a wall. I have been following some of the GIMP tutorials on the site, but I am constantly running into a blockage when I am asked to create an Alpha Channel for my layer.

I have been following Photoshop Map Making Tutorial 3 (Authentic Maps).pdf, a tutorial written by Jeremy Elford.

Here is the quoted section I am trying to follow. I feel like I am missing something though.

"1:0 first thing is we are going to create an alpha channel
select layer with map > Ctrl+A (select all) > Ctrl+C > Channels tab > create new alpha layer > Ctrl+V to paste
in the new channel you just created that's called 'Alpha 1' by default.

1.1: back to your layers tab
Create new layer > Get a tan brown as foreground colour > Edit > Fill > foreground Colour - this will end up
as the light brown area in the image below...
(You could go with any other colour - or keep it as a line drawing on white paper - as you would see in any
novel. To do this you'll want to ignore the bits to fill in colour, or at the end desaturate the image and adjust
levels)

1.2: Back to Channels tab
Hold Ctrl+Left Click (with your mouse - I might also refer to this as 'Ctrl+L click' ) on your map alpha. We do
this to create what is known in Photoshop as a 'Selection set' . By doing this step, we create one which we'll
use to create the outline version of our map (see below compared to above)

1.3: Back to layers. Create new layer,get a dark brown as your foreground colour - for the line work colour.
Again could be any colour you like if you have a different colour scheme.
Edit>Stroke>1 pixel You should see the line work now. It used the selection set from your Alpha channel as
mentioned above. Selection sets and Alpha channels are handy things in PS and used often. In this case,
though it's important to use the alpha channel because it will use the varying shades of grey which you may
note is effective for the rivers on the image below, that they are lighter as they get further inland."


I am working from this image, which I rendered following some of RobA's tutorials.

Project1b.png

After creating my Alpha Channel, my image changes coloration a bit, with the white turning a dark grey. Is this the appropriate response?

Here is a screenshot of my layers tab and UI setup.

Layers Example.png

Here is what my channels tab looks like after I have created the "Alpha Channel."

Channel Example.png

Once I am at this point, it seems I am unable to manipulate the color scheme like the PDF suggests Upon switching back to the layers file I am unable to use the fill tool. Any help or thoughts are much appreciated.

Thanks.