Terrain/Irrigation Change Malfunction

When I try to change terrain for making a scenario, it's ok, however, when I try to alter the irrigation icon, it malfunctions and blends in with the replacement, I've tried manually replacing the icon on terrain.bmp in the folder, however that makes it worse, when that happens it inverts all the colours and I have to remove the entire file and revert to the original. In addition, when I try to change irrigation back to the original on the FW editor, it doesn't work and reverts back to the blended icons. So what's going on?

Here is an example.

Are you sure you save your new icons file under the correct format?
It's been a while, but I think you have to use only 8-bit color palette or 87a non-interlaced GIF for the graphics to work in Civ2.

I don't mean to be rude, but can you describe that in laymans terms?

Your best bet is to use GIMP (free program) to edit those files and export them without interlace and without gif comment. Those two options will appear when you try to export the file after making your changes; by default interlace is disabled so you only need to uncheck the box with gif comment.

Under win xp, the old paint used to do the job but apparently they changed something later and at this point win7 and later versions of paint don't save the file properly.