GIMP :: Changing White In Foreground To A Color?

I can crop images, resize, and do a few other things but that is about the extent of my skills.

I am currently attempting to theme some images in an Android ROM but I'm not able to change the colors the way I want. Essentially I have a bunch of images with transparent backgrounds and white in the foreground. I simply want to swap out the white for another color (red, green, blue, whatever).

I have attached a sample image that I am working on. How on earth do I change the white to red (FF0000) for example? I tried using the select by color tool and clicking in the white area. Then I changed the foreground color to FF0000 and tried to paint into it. It doesn't seem to do anything but paint more white?

Some options were completely disabled for my image. For example, I went to Colors > Map and found that both Color Exchange and Rotate Colors are disabled. Why?

P.S. I have roughly 200 images that I need to perform this action on (and I may even do this with multiple colors -- create a blue set, a red set, etc.) so if there is some way to automate this process I would love to know. I'm a software developer and run Linux so I typically just write bash scripts for tedious tasks such as these. I know there is script-fu in gimp but I'm not familiar with it. Can I just call gimp within a bash loop and pass it some option to do this color change and save the new image for me?