I use the 5 Liter C-41 Tetenal Kit all the time. I haven't seen the *mixed* Color Developer look like that yet, but I have with others, long out-of-date. I would suspect oxidization. How old are the chemicals, and how long have the individual bottles been open? Were the plastic bottle seals intact when you received the kit?
I once purchased what I believed to be a NEW Photocolor C41 Kit from a supposedly reputable retail store. When I got it home ALL the bottles had been opened, were about half full, and the sensitive "Part B" was FRIED - oxidized to @#$%@#$.
I returned it, indignant, and they replaced the kit. All they would say after an additional 50 mile trip, was "Oh, things like that happen, once in a while".
Come to think of it ... I remember another instance, from another store... When a chemistry kit was opened, and I discovered one of the bottles was holed, had leaked and was empty. I returned that kit, and it was replaced. What happened to the defective kit? - Right back on the shelf, waiting to be resold, as is, with no indication to the next buyer.