Soontir Fel's core character changes very little in this incarnation, actually. He still has a strong, overriding sense of loyalty and duty, and is still a cold and rather withdrawn figure.
I portrayed Fel in the Union's standard navy uniform (based on the Rebel officers' uniforms seen in "Return"), basically because there wouldn't be any other place to show what the Union's real uniform looked like (rather than Han or Leia's "darked down" version of it).