Hello, as you may now cancer can only be diagnosed by looking at the cells of the area in question. Certainly, we can get a suspicion for cancer by assessing the gross appearance of the area in question. This means that although looking at Blue's nose I don't think it looks very aggressive to be considered a cancer, we are unable to tell unless we sample that area.
Cats can get pigmentation changes with age, so this may very well be a normal change associated with his age and nothing you need to be concerned with.
I would recommend monitoring the area for progression of this pigmentation change or any evidence of mass, ulcer, or thickening of the nose which would be more concerning for a cancer.