In addition to the BROWN v Yellow,
there were differences in the handling of BRIGHT BLACK.
(Joe Campbell borrowed a "real" CGA card from me when he
found out that his Corona did not give the same color as IBM.)
Surely any differences were in the monitor. Given that there are 16
possible colours, and 4 bits on the output DE9, it's hard to see how the
purely-digital card could make any difference.
-tony