...More or less what it says in the title. Basically, I just want to open up one of the image files and alter the color scheme to improve the usability (especially for color blind players). Is there a quick way to do this?

The VASSAL module is a zip file. Just rename it to somthing.zip and open it.

Thanks!

The editions that you make in your file will only be visible by you, though. If you want others to share this benefit, you have to share that modified version of the module.