Oxidized Color developer usually will have the effect of not producing a decent "Black". The remaining colors will degrade as well, but the "graying" of that which should be black is most noticeable.

That said, If the mixed color developer is decidedly "dark" it is most probably, shot.

Be careful of Color Developer "carry-over" into the Bleach-Fix. That is why shortstop is necessary in RA-4 processing.