GIMP Version: 2.8.14
Operating System: Windows
GIMP Experience: Basic Level

---

I tried doing this in Corel PHOTO-PAINT, which can probably do the job—but not so long as I'm the one using the program. Likewise, I imagine GIMP can help me remove the color Crayon marks (yellow, red, and blue) from a coloring sheet while leaving black outlines alone—but I'll never figure out how in a thousand lifetimes. I'm just that dull-witted. I know I can carefully erase between outlines, but that will take more time than I have to spend. Surely, there is a way smart people would do the job in a minute or two?

I'm no good at layers. I understand the concept at a rudimentary level, but have no experience. I'm usually just tweaking portraits and photos of student artwork. This time, I want to clean up a coloring sheet so my kids can use it in class.

If anyone out there knows how to do something like this and has time to walk an ape through the process, I'd be much obliged.

Thanks, and have a fantastic weekend!

Might be an idea if you can post the picture or part of. Then we can give you our workflows to what we did.
You will have to have 5 posts I think to post a picture, here is 1, introduce yourself in the introduction forum and ask a couple other questions or reply to ones already started.

If they are actual solid colors (no gradients), Gimp can remove them with Colors>Color to Alpha.
This grabs solid colors and leaves transparency.
Or you can try
Select>Select by color
Make the color 6 zeros, 000000 Which is Black, and then go to Select>Invert>
Then Edit>Delete or Edit>Clear.
That should keep or retain the black color and remove everything else.Keeping your outlines.
Hope that helps! If we had an image of your coloring book that would be most helpful.
Welcome to Gimp Chat by the way.

Also the newest Gimp install is 2.10.38. Which in my opinion is better then 2.8.