Is the skin of the bird in question black, or just the comb? An Araucana x Warren would not usually be fibro, but I've found that a melanised bird can sometimes have a dark wash to their comb.
If the skin is also black, then the bird is fibro (and likely with a different breed mixed in); you will often see a burgundy cast to the comb as the bird reaches maturity, particularly if the bird is impure for fibro (which is likely). You can therefore identify any males through that purple colour, as pullets will not get it until POL. I'd like to see photos too, if I may.