I agree with mrpnut...very nice job. As for answering your question, it all really depends on what program you're using for the image editing. If it's GIMP, then in toolbox, there should be a slider with the word "Opacity" somewhere next to it. Just as an example of what I would do (and have done), choose the same color you used for the rings, slide the opacity to about 75%, color the pixels where the jagged edges are the most noticeable, drop it again to about 50% and color a pixel or two next to it. The nice thing with GIMP is it'll show you in real-time what the changes you made will look like, both in the "Undo History" window, as well as in the top left corner of the main editing window. Of course, this example would just be a quick and dirty way of fixing the problem, but gives you the basic steps necessary. For instance, depending on how adamant you want to be on the rings looking like perfect circles, you may end up using several different opacity levels (maybe you step in increments of 5 or 10 instead of 25, or even 1 or 3 or some random number each time). Anyway, the key idea is to play around with the opacity setting until you get what you're looking for.
If you're using a different editing program (such as Paint.net or some version of Adobe Photoshop), then I would look for some sort of color opacity or transparency setting in there, and follow the same steps above. If your photo editor doesn't have a color opacity/transparency setting, then hit me back, as I still have an idea or two up my sleeve
.
Also, I know it's for a different phone, but you can also give a look at the guide I'm working on about this very subject, found
here. The UOT Kitchen part may be different (I'm not sure as I haven't gotten to mess around with the internals of a device with ICS or better), but most of the concepts should otherwise translate over. In the guide, particularly the section titled "Editing standard photos", I address the part about coloring the entire picture all at once vs. coloring each element individually, and how to do both.
EDIT: Sorry, just dawned on me that you may have meant coloring
several pictures all at once instead of individually. Unfortunately, I don't know of any way of batch-editing photos other than using a website like UOT Kitchen, and even then sometimes I still have to go through each picture individually and tweak something.
Good luck, and let us know how it goes.