Why do yellows have a "reputation"???

I got my first Syrian (since childhood...so about 20+ years later!) at the start of this year....I wasn't even sure what his "official" colour was when I got him but I now believe he's a yellow. Talking to Holly and various other people, I'm starting to learn that yellows have a bit of a reputation for being a bit jumpy....I was just wondering if any of you can shed any more light on it for me so it'll help me understand my boy a little more....????

This is him - Custard (yellow, sweet - and a bit thick!). His coat's come through more since these photos:
http://i262.photobucket.com/albums/ii88 ... ubs005.jpg
http://i262.photobucket.com/albums/ii88 ... 008003.jpg