CompacTape I and CompacTape II were completely
identical
in every detail - except for for the colour of the name on the case.
Usually The "CompacTape" label was brown; the "CompacTape II"
was usually blue. Oh yes, DEC charged a fair bit more for the tape
This convention -- brown for low-capacity, blue for high capacity -- was
used on other DEC media of course (RL01 and RK06 packs have brown
handles, RL02 and RK07 packs have blue handles). Although in that case
there are differences other than the colour.
-tony