Thanks for trying Molly.
Just to be sure, as I wasn't 100% clear from your post, did you use the plugin from the first post (Colors-Colorization)?
viewtopic.php?f=9&t=1625#p20167

I tried with the fu script that Graechan posted to create the layer, then I painted stripes on that new layer before running Colors-Colorization, but I still didn't see anything other than what Molly posted.

Er...
I need a piece of advice on windows installation, I placed the two files blas.dll and colorize.exe in my plug-ins user folder and nothing shows up (or if it do shows up I don't know where it is supposed to appear).

Colorize-Gimp should be in your, Colors menu, Colorization...
If you decide to use "FU_colorize-prep.scm", Script-Fu menu, Prepare for Colorize.

Colors/Colorization, so it shows up, thanks !

It seems promising, as well as intriguing (is this edge detection?), I managed to crash the plugin twice when using it, so far I've seen that:
- two images opened=crash
- layer named with an accented letter=crash (problematic for french users where some copied layers are automatically named calque copié)

Thanks for the script Graechan.

Where can I download this plugin for windows? I downloaded the colorize zip and installed it into the plugin folder of gimp 2.8 but it does not show up anywhere. There were only two files when I extracted the zip file. Please help!! Thank you in advance.

Thank you very much. I do see that on my menu. Do I need to delete the colorize files that I downloaded? Will they cause a problem if left in the plugin folder?

I believe the default is a different program. I was trying to get the one described on page 1 where you put the color stripes on your image. I could not get the default program to work.