fill in a bash script

Working with bash and gimp on linux here.
I am looking for the scriptname and parameters for the fill bucket.
To be sure you understand what I am talking about:
http://docs.gimp.org/2.2/en/gimp-tool-bucket-fill.html

I know that I should be using `gimp-bucket-fill`

Searching I found things like
gimp-bucket-fill layer filltype NORMAL-MODE 100 0 FALSE 0 0

I could do it by trial and error and still it would be nicer if there
was some sort of list that gave you all the options and explanation to
day what does what.
I also do not see what the colour should be that one wants to use, or is
that selected in a different way?

I have looked, but found nothing. I must have searched on the wrong
words and the wrong place. :-(


Here some extra information on what I intend to do, as it might inspire
others:

I have a 1920x1200 image. I take the average colour with:
houghi@[EMAIL PROTECTED]
 : convert 0007.jpg -filter Box -resize 1x1 -depth 8 txt:-| \
tail -n1|awk '{print $NF}'

rgb(123,90,77)

That will standard be the colour I would use in the bucket to make an
overlay.
By randomness I will select a number between 60 and 90 to be the
opacity.
By randomness I will also make the colour darker or lighter by adding or
subsctracting X% from each of the numbers in the colour.

That way I can easily process several thousand pictures and turn them
into backgrounds. I do not like clear pictures as background and that is
what I currently have the most of.

houghi
-- 
This was written under the influence of the following:
|  Artist : Anastacia
|    Song : ***y Single
|   Album : Anastacia