From the Phase II bible:
The refurbished Enterprise is slightly changed, just enough for the audience to say "Yes, it is the Enterprise, and even lovelier than before..."
I wonder if the Phase II versions of the interiors might have retained more of a TOS look, despite the updated TMP interfaces having originated with the abandoned series. Maybe the Phase II versions of certain sets would have retained more of the TOS color scheme? Or maybe they might have had a rougher edge to them? (Presumably the already half built sets got all got a top-to-bottom retrofit when it was decided definitively to blow them up to big screen size.)