Colour problem when capturing a png of the top panel of the screen

Question

I want to capture a window as a png from within a bash script, using the window's ID. In this case, the window is the top panel.  Using gnome-screenshot the colours are true, as per this image... (this image is not the same size as the following image, so ignore the dark line at the bottom)

However when I capture the panel via import, or xwd + convert, I get the following image..

Why would I be getting this colour aberration?

import and convert both belong to the imagemagick package...

I haven't found anything else in the Ubuntu repository which can capture a window by its ID... so I'm stuck. (gnome-screenshot doesn't have the feature)... It would be nice to know what is going on here (eg, is is something to do with transparent images, which I know very little about)...but in any case, just a recommendation of a workaround capture utility may do the trick ... it must be able to capture a window by it's ID.   

Here is an example of how I make and view the image capture.

import -window "$(wmctrl -l |grep "Top Expanded Edge Panel" |awk '{print $1}')" screen.png  
display screen.png

Answer 1

For making screens from console there is also scrot. As it is not a tool from imagemagick package I think that there is a chance that colors will be ok.

There is one problem - scrot can only take sceenshot of full screen, so we will take screenshot of full screen and then cut out area of window that we need. Of course for cut it out we will not use imagemagick but tools from netpbm package.

#!/bin/bash
unset x y w h
eval $(xwininfo -id $(wmctrl -l |grep "Top Expanded Edge Panel" |awk '{print $1}') |
        sed -ne "s/^ \+Absolute upper-left X: \+\([0-9]\+\).*/x=\1/p" \
             -e "s/^ \+Absolute upper-left Y: \+\([0-9]\+\).*/y=\1/p" \
             -e "s/^ \+Width: \+\([0-9]\+\).*/w=\1/p" \
             -e "s/^ \+Height: \+\([0-9]\+\).*/h=\1/p" )
scrot scrot.pnm
    < scrot.pnm pnmcut -left $x -top $y -width $w -height $h | pnmtopng > scrot_cropped.png
display scrot_cropped.png

Could you check if with scrot you could make screenshot with unchanged colours? If yes that script should do the work and take screen of window that you want....

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Script inspired on answers of @fred: How do I find the window dimensions and position accurately including decorations? and @JRW: Oneliner for slicing an image?