[Happy Monkey]

Yes; that's what BigV was saying. I was offering an explanation for why Bruce's picture increased in size after changing the color. JPG compression artifacts add even more edges and complexity to the image, in a way that decreases the file size during the initial encoding. But when the file is loaded into an editor, all of those artifacts become data, and when saving it off as a JPG again, they are treated as real complexity, making the JPG encoding work harder. Another reason the file size increased may be differing JPG quality settings between the initial and secondary encodings.

My second note was more of an aside; I don't think JPG does it. But, much as an MP3 throws away information about sound that humans have trouble distinguishing, an advanced image format could theoretically throw away a bit of red and blue in favor of green, to match the human eye. If such a theoretical image were primarily green, it wouldn't be able to throw as much data away.