DST formats lack color information. As a consequence most all software will randomly assign colors to each place where the thread colors are changed. Due to the way the PhotoEmbroidery process works, this becomes very apparent. There is nothing to worry about, but it can at times make things more difficult to view or make minor alterations to.
DST and many other formats which store only the worker data (the commands which run the embroidery machine), to the machine, thread is thread, it only needs to know when it switches to the next thread not what color that is. Which is fine for the machine, but annoying for the visualization of embroidery strongly dependent on visualization.