Civilization II for the Mac uses a funny graphics system. It utilizes a non-standard color palette in the PICT files it uses. Thus, if you try to edit the Units.pict and save the file, it will look horrible. Good news is that there are a couple of workarounds to this problem..
Edit the file as a .gif - then convert it to .pict using Graphic Converter
This is one solution. Here is a pristine copy of the Units.gif file from Civ II. Download and edit it as you please in gif format, then save the file as a .gif file.
Finally, convert it to a .pict file. A problem occurs if you try to convert the file back to .gif after it's a .pict file. You'll end up with a screwed up file, so don't.
Use the Civ II PAL app
This is a more tricky solution. Civ II PAL is an application that changes the color palette to a more standard one. This is useful if you want to do a minor change to the e.g. Units.pict file.
I have found that it only seems to work well with a free image-editor called Ansel. Others appear to mess up the color palette. Both, Civ II PAL and Ansel can be found in our download section.