When tracing with colours being chosen automatically, the colour is only chosen on 'mouse down' - where the tool first touches the canvas. (The exception is the new glitter in ArtRage 2.2, which chooses the colour for every glitter particle all the time).
So it could be choosing a slightly different colour each time from the source image.
Regarding posting traced work - go right ahead. It would be polite to put a note saying it's a traced artwork as well.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"