Buddy's coat

It's been more than a year since Buddy was adopted and yet most of the other cats do not accept him. He is neutered and is healthy. He is an orange tabby with some white on his chest and face. In the photos by my user id, he is in the lower left picture.
The other day I saw a cat resting on the perimeter wall. It was Buddy but I did not recognize him. His coat was more orange than usual and no trace of white. It was a sunny day. Is it possible that he is not being accepted because his coat changes under different lighting? I've noticed that when he is "attacked" the aggressor seems to realize he is fighting a familiar cat. Most of the time I interfere during the fights because Buddy does not stop once he is challenged. However, there are times they cease fighting as suddenly as they start.
I know cats identify others by scent but is it possible that sight affects recognizing friend or foe?

I think what you saw was either another cat who looked a lot like Buddy (it happens), or the effect of sunlight on him when he was on the wall. But in any case, cats recognize each other by smell, and/or sound, and they are color-blind (only 'see' certain colors well, and others are grayed out), so I really doubt that a bit more or less orange would make a difference to other cats.