Do you use a compositor? (Transparent windows, etc.) If you don't, this is easy.
import -window root -crop 1x1+100+200 foo.txt
Here you put in coordinates for 100 and 200. This gives you something like
# ImageMagick pixel enumeration: 1,1,65535,srgb
0,0: (15420,15420,15420) #3C3C3C3C3C3C srgb(60,60,60)
which you can awk into submission.
If you DO use a compositor, neither import nor xwd can see the transparency
(here they fill it with black), so you may have to use a different program.
GIMP works, but I don't know the batch mode curse to take a screenshot.
scrot may also work, but it doesn't come with Slackware.