I am a programmer so I'm going to try to look at the code and see if I can add it myself. C# is my main language but I know java and the Android SDK. But if somebody who already has experience with the code thinks they can add it quickly, be my guest.
It would be nice to have a highlighter tool. It would be a vector graphic that just multiplies the current color over the vectors below it. So it highlights it without overwriting it. I don't know how complicated that is since I haven't looked at the code.
Another alternative if the highlighter is too complicated, would be a recolor paintbrush. Any vector you write over becomes the current color. I think that should be pretty simple.
The whole point of these suggestions is that I don't like changing colors while I am taking notes. I'd rather look at my notes afterwards and change the color then to highlight important sections. I know you can underline things but that tends to look pretty ugly for me.
The last idea is a section tool for moving around large chunks ot text. The tool itself could be drawn just like the image box with a handle in the center for moving the text. Once you click outside of the box after moving it, the box disappears and the text is in it's new location. A lasso tool would be more useful but I think having a box at least would be good enough for most situations.