When using a ferricyanide bleach, it is absolutely required to use a stop bath, preferrably a clearing stop bath, followed by a wash, between the developer and bleach or the bleach will oxidize the developer and you will get a brown stain on your negatives. It is not necessary with Flexicolor bleach. You should also follow a ferricyanide bleach with a good long wash to prevent sulfurization of the fixer by the bleach, forming a fog on the film. I have used a ferricyanide bleach and it works well but as you can see it adds more steps and time to the process.
Originally Posted by keyofnight
Looking at your film, I have doubts that the problem is under-bleaching. I have never seen film that is severely under-bleached, but I can't imagine the unexposed areas of the film being as dark as they are due to it, since little or no silver would form there. As someone else said, the problem lies elsewhere.