A familiar is a spiritual bond between you and the animal, you can't train it to be one. If the cat sees spirits and is afraid, it will hiss, I don't think you can train fear of spirits out of an animal. If the cat reacts like this, then it is certainly not your familiar. Observe it when you cast your circle, does it walk the perimeter, watch you from a distance, or act obliviously normal. Just because the animal can see a spirit doesn't make him a familiar. My cat sees spirits, he also walks through my circles so is put in the bedroom with the door closed.
Colour doesn't matter. It's an old superstition black animals like crows, ravens, dogs and cats as well as rats and toads were witches in disguise, or spies for them, aka familiars. This isn't true, just scared people whose stories has been passed down. It's similar to assuming any skin blemish is a sign of evil.